Repeat Surgery after Percutaneous Endoscopic Lumbar Discectomy for Adolescent Lumbar Disc Herniation: A Multicenter Observational Study.

OBJECTIVE: The reported date in the repeat surgical intervention for adolescent lumbar disc herniation (ALDH) after percutaneous endoscopic lumbar discectomy (PELD) was quite scarce. This study aims to introduce cases of repeat surgeries after PELD for ALDH and assess the incidence, chief causes, repeat surgery methods, and surgical outcomes of repeat surgeries after PELD for ALDH. METHODS: A retrospective multicenter observational study was conducted on patients undergoing repeat surgeries after PELD for ALDH at four tertiary referral hospitals from January 2014 through August 2022. The incidence of repeat surgeries, chief causes, strategies for repeat surgeries, and timing of repeat surgeries were recorded and analyzed. The clinical outcomes were evaluated by the Numeric Rating Scales (NRS) scores and the modified MacNab criteria. Statistical analyses were performed with the Wilcoxon signed-rank test. RESULTS: A total of 23 patients who underwent repeat surgeries after PELD for ALDH were included. The chief causes were re-herniation (homo-lateral re-herniation at the same level, new disc herniation of adjacent level). The repeat surgery methods were revision PELD, micro-endoscopic discectomy (MED), open discectomy and instrumented lumbar inter-body fusion. The NRS scores decreased significantly in follow-up evaluations and these scores demonstrated significant improvement at the last follow-up (p < 0.002). For the modified MacNab criteria, at the last follow-up, 18 patients (78.26%) had an excellent outcome, and the overall success rate was 86.95%. CONCLUSION: This study's data suggest that young patients who underwent repeat surgery improved significantly compared to baseline. The chief cause was re-herniation. Revision PELD was the main surgical procedure, which provides satisfactory clinical results in young patients who underwent repeat surgeries.

Endoplasmic reticulum stress-mediated autophagy alleviates lipopolysaccharide-induced nucleus pulposus cell pyroptosis by inhibiting CHOP signaling in vitro.

Pyroptosis, a newly discovered pro-inflammatory programmed necrosis of cells, serves as an initiating and promoting event that leads to intervertebral disc (IVD) degeneration (IDD). Endoplasmic reticulum stress (ERS) and autophagy are vital regulatory mechanisms of cellular homeostasis, which is also closely related to IDD. However, the role and relationship of ERS and autophagy in the pyroptosis of nucleus pulposus cell (NPC) are not well understood. In this research, we aimed to elucidate the role and mechanism of ERS-C/EBP homologous protein (CHOP) in lipopolysaccharide (LPS)-induced cell pyroptosis and determine its interaction with autophagy. ERS and autophagy inducers or inhibitors were used or not in the preconditioning of rat NPCs. Cell viability, pyroptosis-related protein expression, caspase-1 activity assay, and enzyme-linked immunosorbent assay were performed to observe rat NPC pyroptosis after the treatment of LPS. Activation of the ERS pathway and autophagy were assessed by quantitative real-time PCR, western blot analyses, and immunofluorescence staining assay to classify the molecular mechanisms. Our results showed that LPS stimulation induced NPC pyroptosis with concomitant activation of the ERS-CHOP pathway and initiated autophagy. Activation of the ERS-CHOP pathway exacerbated rat NPC pyroptosis, whereas autophagy inhibited cell pyroptosis. LPS-induced cell pyroptosis and CHOP upregulation were negatively regulated by autophagy. LPS-induced autophagy was depressed by the ERS inhibitor but aggravated by the ERS inducer. Taken together, our findings suggested that LPS induced NPC pyroptosis by activating ERS-CHOP signaling and ERS mediated LPS-induced autophagy, which in turn alleviated NPC pyroptosis by inhibiting CHOP signaling.

Interpretable Machine Learning Model to Predict Bone Cement Leakage in Percutaneous Vertebral Augmentation for Osteoporotic Vertebral Compression Fracture Based on SHapley Additive exPlanations.

STUDY DESIGN: Retrospective study. OBJECTIVES: Our objective is to create comprehensible machine learning (ML) models that can forecast bone cement leakage in percutaneous vertebral augmentation (PVA) for individuals with osteoporotic vertebral compression fracture (OVCF) while also identifying the associated risk factors. METHODS: We incorporated data from patients (n = 425) which underwent PVA. To predict cement leakage, we devised six models based on a variety of parameters. Evaluate and juxtapose the predictive performances relied on measures of discrimination, calibration, and clinical utility. SHapley Additive exPlanations (SHAP) methodology was used to interpret model and evaluate the risk factors associated with cement leakage. RESULTS: The occurrence rate of cement leakage was established at 50.4%. A binary logistic regression analysis identified cortical disruption (OR 6.880, 95% CI 4.209-11.246), the basivertebral foramen sign (OR 2.142, 95% CI 1.303-3.521), the fracture type (OR 1.683, 95% CI 1.083-2.617), and the volume of bone cement (OR 1.198, 95% CI 1.070-1.341) as independent predictors of cement leakage. The XGBoost model outperformed all others in predicting cement leakage in the testing set, with AUC of .8819, accuracy of .8025, recall score of .7872, F1 score of .8315, and a precision score of .881. Several important factors related to cement leakage were drawn based on the analysis of SHAP values and their clinical significance. CONCLUSION: The ML based predictive model demonstrated significant accuracy in forecasting bone cement leakage for patients with OVCF undergoing PVA. When combined with SHAP, ML facilitated a personalized prediction and offered a visual interpretation of feature importance.

Scientific Bibliometric and Visual Analysis of Studies on Autophagy in Intervertebral Disc Degeneration Based on Web of Science.

OBJECTIVE: To analyze the current research trends and potential mechanisms related to the role of autophagy in intervertebral disc degeneration (IVDD) and to provide new ideas for future research in this field. METHODS: All articles on IVDD and autophagy were retrieved and extracted from the Web of Science (WoS) core collection database. The results were evaluated and visualized using the bibliometric Web site, CiteSpace, and VOSviewer software, including annual articles published, countries, institutions, authors, journals, research areas, funding agencies, citations, and keywords. RESULTS: From January 1, 2011, to December 31, 2022, 323 reviews and original articles were included, and the overall trend in the number of articles was increasing rapidly. China and the United States were the countries with the most scientific research achievements. The 323 articles received a total number of citations of 6949, with an H index of 43 and an average citation of 21.51. The top publication country, institution, author, journal, research area, and funding agency were China, Huazhong University of Science and Technology, Cao Yang of Tongji Medical College, Oxidative Medicine and Cellular Longevity, cell biology, and National Natural Science Foundation of China, respectively. Most of the keywords were associated with the mechanisms and regulatory networks of autophagy. In addition, with increasing evidence showing the key role of autophagy in IVDD, therapy, signaling pathway, and mitophagy are emerging as new research hot spots that should be paid more attention. CONCLUSIONS: This study provided a scientific perspective on autophagy in IVDD and elucidated the current research status and hot spots in this field. The mechanism of autophagy and the application of regulating autophagy in the treatment of IVDD deserve further research.

Which Criterion for Wound Drain Removal is Better Following Posterior 1-Level or 2-Level Lumbar Fusion With Instrumentation: Time Driven or Output Driven?

STUDY DESIGN: Case-control study. OBJECTIVES: To compare the outcomes of 2 different criteria (time driven and output driven) for wound drain removal and identify which one is better. METHODS: 743 patients who underwent posterior lumbar fusion with instrumentation involving 1 or 2 motion segments were enrolled in this study. Based on the different criteria for drain removal, the patients were divided into 2 groups. The drains were discontinued by time driven (postoperative day 2) in group I and output driven (<50 ml per day) in group II. Demographic characteristics, perioperative parameters and clinical outcomes were compared between the 2 groups. RESULTS: The demographic characteristics in both groups were comparable. The postoperative drain output, total blood loss, postoperative timing of ambulation, and postoperative duration of hospital stay in group I were lower than those in group II (P < 0.001). There was a higher proportion of patients requiring postoperative blood transfusion in group II, but not to a level of statistical significance (P = 0.054). There was no statistical significant difference in the incidence of surgical site infection (SSI) or symptomatic spinal epidural hematoma (SEH) between the 2 groups (P > 0.05). CONCLUSIONS: This study reveals that there are more benefits of wound drain removal by time driven than that by output driven for patients undergoing posterior 1-level or 2-level lumbar fusion with instrumentation, including less postoperative drain output, less total blood loss, earlier postoperative timing of ambulation and less postoperative duration of hospital stay without increasing the incidence of postoperative SSI or symptomatic SEH.

The Mini-Open Wiltse Approach with Pedicle Screw Fixation Versus Percutaneous Pedicle Screw Fixation for Treatment of Neurologically Intact Thoracolumbar Fractures: A Systematic Review and Meta-Analysis.

OBJECTIVE: The purpose of the present study was to compare the clinical outcomes and complications between the mini-open Wiltse approach with pedicle screw fixation (MWPSF) and percutaneous pedicle screw fixation (PPSF) in treating neurologically intact thoracolumbar fractures. METHODS: We comprehensively searched PubMed, Web of Science, Embase, and the Cochrane Library and performed a systematic review and meta-analysis of all randomized controlled trials and retrospective comparative studies assessing these important indexes of the 2 methods using Review Manager, version 5.4. The clinical outcomes are presented as the risk difference for dichotomous outcomes and the mean difference for continuous outcomes with the 95% confidence intervals. Heterogeneity was assessed using the χ2 test and I2 statistics. The study was registered with PROSPERO (CRD 42021290078). RESULTS: Two randomized controlled trials and six retrospective cohort studies were included in the present analysis. The percutaneous approach was associated with less intraoperative blood loss compared with the mini-open Wiltse approach. No significant differences were found in the total length of the incisions, hospitalization time, postoperative visual analog scale scores, postoperative Oswestry disability index, postoperative Cobb angle, postoperative Cobb angle correction, postoperative Cobb angle correction loss, accuracy rate of pedicle screw placement, and postoperative complications between MWPSF and PPSF. However, the incidence of facet joint violation was significantly higher in the PPSF group. In addition, MWPSF was associated with a shorter operative time, shorter intraoperative fluoroscopy time, lower hospitalization costs, better postoperative vertebral body angle and percentage of vertebral body height compared with PPSF. CONCLUSIONS: Both MWPSF and PPSF are safe and effective treatments of neurologically intact thoracolumbar fractures. Nevertheless, our results have indicated that MWPSF might be the better choice, because it has a shorter learning curve and decreased facet joint violation, operative time, hospitalization costs, and radiation exposure. In addition, MWPSF was associated with better improvement of the postoperative vertebral body angle and percentage of vertebral body height.

GATA4 promotes the senescence of nucleus pulposus cells via NF-κB pathway.

PURPOSE: Cell senescence plays a vital role in intervertebral disc degeneration. The regulatory mechanism of the cellular senescence of nucleus pulposus cells has not been fully elucidated. A recent study identified GATA4 as an emerging regulator of IMR90 cellular senescence. However, whether GATA4 controls senescence in nucleus pulposus cells still needs to be explored. METHODS: Nucleus pulposus cells were exposed to acidified medium mimic the acid environment of intervertebral disc degeneration. RESULTS: We found that GATA4 protein expression was significantly upregulated in older rats and nucleus pulposus cells undergoing stress-induced aging. Moreover, the data indicated that inhibition of GATA4 significantly inhibited the senescence of nucleus pulposus cells cultured under acidic conditions and that over expression of GATA4 promoted a senescence phenotype. The NF-κB pathway has been confirmed in this study to play a role in the regulation of nucleus pulposus cell senescence by GATA4. By using the NF-κB pathway inhibitor, PDTC (100 µmol/L), significantly decreased the IL-6, matrix metallopeptidase (MMP)-2, MMP-3, MMP-9, MMP-13, ADAM metallopeptidase with thrombospondin type 1 motif (ADAMTS)-4, ADAMTS-5 expression level, and increased Aggrecan and typeⅡcollagen expression level in GATA4 transfected nucleus pulposus cells compared with the group in the absence of PDTC. CONCLUSION: This outcome suggested that GATA4 might play a significant role in nucleus pulposus cell senescence through the NF-κB signaling pathway, and GATA4 is a promising target for intervertebral disc degeneration treatment in the future.

Unfolded protein response alleviates acid-induced premature senescence by promoting autophagy in nucleus pulposus cells.

Acid-induced cellular senescence is a critical underlying mechanism of intervertebral disc (IVD) degeneration (IDD). Acid stimulation activates a variety of biological changes including autophagy, endoplasmic reticulum stress, and related unfolded protein response (UPR), which are important regulators of cellular senescence. However, the precise mechanism of acid-mediated UPR and autophagy in nucleus pulposus cell (NPC) senescence has not been fully elucidated. In this study, we used acid to mimic the acidic microenvironment of IVD, and rat NPCs were cultured with or without autophagy or UPR signaling small-interfering RNAs. The related proteins and genes were assessed by immunofluorescence staining assay, Western blot analyses, and quantitative real-time polymerase chain reaction to monitor the activation of these signals and classify the molecular mechanisms underlying the correlation between autophagy and UPR pathway. Cell cycle analyses, senescence-associated ß-galactosidase staining, gene expression, and immunoblotting analyses were performed to observe NPC senescence. Results showed that acid stimulation not only induced NPC senescence, but also initiated UPR and autophagy. Silencing the binding immunoglobulin protein signaling of UPR or autophagy signaling promoted rat NPC senescence. Knock-down of the UPR also blocked NPC autophagy. Taken together, UPR inhibits NPC senescence under acidic condition by activating autophagy. Hence, UPR-dependent autophagy could be an effective biologic target for the treatment of IDD in the future.

A20 of nucleus pulposus cells plays a self-protection role via the nuclear factor-kappa B pathway in the inflammatory microenvironment.

AIMS: Inflammatory response plays a pivotal role in the pathophysiological process of intervertebral disc degeneration (IDD). A20 (also known as tumour necrosis factor alpha-induced protein 3 (TNFAIP3)) is a ubiquitin-editing enzyme that restricts nuclear factor-kappa B (NF-κB) signalling. A20 prevents the occurrence of multiple inflammatory diseases. However, the role of A20 in the initiation of IDD has not been elucidated. The aim of the study was to investigate the effect of A20 in senescence of TNF alpha (TNF-α)-induced nucleus pulposus cells (NPCs). METHODS: Immunohistochemical staining was performed to observe the expression of A20 in normal and degenerated human intervertebral discs. The NPCs were dissected from the tail vertebrae of healthy male Sprague-Dawley rats and were cultured in the incubator. In the experiment, TNF-α was used to mimic the inflammatory environment of IDD. The cell viability and senescence were examined to investigate the effect of A20 on TNF-α-treated NPCs. The expression of messenger RNA (mRNA)-encoding proteins related to matrix macromolecules (collagen II, aggrecan) and senescence markers (p53, p16). Additionally, NF-κB/p65 activity of NPCs was detected within different test compounds. RESULTS: The expression of A20 was upregulated in degenerate human intervertebral discs. The A20 levels of NPCs in TNF-α inflammatory microenvironments were dramatically higher than those of the control group. TNF-α significantly decreased cell proliferation potency but increased senescence-associated beta-galactosidase (SA-ß-Gal) activity, the expression of senescence-associated proteins, the synthesis of extracellular matrix, and G1 cycle arrest. The senescence indicators and NF-κB/p65 expression of A20 downregulated group treated with TNF-α were significantly upregulated compared to TNF-α-treated normal NPCs. CONCLUSION: A20 has a self-protective effect on the senescence of NPCs induced by TNF-α. The downregulation of A20 in NPCs exacerbated the senescence of NPCs induced by TNF-α.Cite this article: Bone Joint Res. 2020;9(5):225-235.

ASIC1a activation induces calcium-dependent apoptosis of BMSCs under conditions that mimic the acidic microenvironment of the degenerated intervertebral disc.

PURPOSE: In the degenerated intervertebral disc (IVD), matrix acidity challenges transplanted bone marrow mesenchymal stem cells (BMSCs). The Ca2+-permeable acid-sensing ion channel 1a (ASIC1a) is responsible for acidosis-mediated tissue injury. The aim of our study was to confirm whether ASIC1a activation induces BMSC apoptosis under conditions that mimic the acidic microenvironment of the degenerated IVD. METHODS: ASIC1a expression in rat BMSCs was investigated by real time-PCR, Western blot (WB) and immunofluorescence. The proliferation and apoptosis of BMSCs under acidic conditions were analyzed by MTT and TUNEL assays. Ca2+-imaging was used to assess the acid-induced increase in the intracellular Ca2+ concentration ([Ca2+]i). The activation of calpain and calcineurin was analyzed using specific kits, and WB analysis was performed to detect apoptosis-related proteins. Ultrastructural changes in BMSCs were observed using transmission electron microscopy (TEM). RESULTS: Acid exposure led to the activation of ASIC1a and increased BMSC apoptosis. The Ca2+ imaging assay showed a significant increase in the [Ca2+]i in response to a solution at pH 6.0. However, BMSC apoptosis and [Ca2+]i elevation were alleviated in the presence of an ASIC1a inhibitor. Moreover, ASIC1a mediated the Ca2+ influx-induced activation of calpain and calcineurin in BMSCs. WB analysis and TEM revealed mitochondrial apoptosis, which was inhibited by an ASIC1a inhibitor, in BMSCs under acidic conditions. CONCLUSIONS: The mimical acidic microenvironment of the degenerated IVD can induce BMSC apoptosis by activating Ca2+-permeable ASIC1a. An acid-induced elevation of [Ca2+]i in BMSCs leads to the subsequent activation of calpain and calcineurin, further resulting in increased mitochondrial permeability and mitochondrial-mediated apoptosis.

A histocytological and radiological overview of the natural history of intervertebral disk: from embryonic formation to age-related degeneration.

PURPOSE: To elucidate the natural history of intervertebral disk (IVD) and characterize its embryonic beginnings and age-related degeneration. METHODS: Coronal sections of embryonic (E13.5-neonatal) and postnatal (4-60-week-old) Sprague-Dawley rat IVD were stained by a series of histological stainings (hematoxylin and eosin, Alcian blue, Picrosirius red, Masson, Periodic acid-Schiff). Growth kinetics within embryonic IVD were evaluated by immunohistochemical staining of Ki67 and proliferating cell nuclear antigen. Postnatal maturation and degeneration of IVD were visualized on radiology by X-ray, CT, and MR imaging. RESULTS: During the formation of rat IVD, inner annulus fibrosus (AF) and cartilaginous endplate (CEP) shared similar cell density, extracellular matrix, and potential of growth kinetics; notochord provided increased and enlarged cytoplasmic vacuoles to generate nucleus pulposus (NP), part of which was retained within CEP. Postnatally, vacuolated notochord cells were reduced by devacuolation, while chondrocytic NP cells increased; cartilaginous layers of CEP were narrowed by vertebrae growth and secondary ossification; fibrotic portion of AF decreased as cartilaginous matrix accumulated and infiltrated outward. In aged and degenerated IVD, large longitudinal fissures were detected near the boundaries between inner and outer AF, whereas both reduced cellularity and accumulated cell clusters were evident within the dehydrated NP; only part of these histocytological changes could be reported on radiology. CONCLUSIONS: By showing that the natural history of IVD is orchestrated by a dynamic histocytological regulation, our study may facilitate better understanding of the developmental defects, cellular heterogeneity, age-related degenerative mechanisms, and biological regeneration of IVD. These slides can be retrieved under Electronic Supplementary Material.

Nuclear factor-kappa B-dependent X-box binding protein 1 signalling promotes the proliferation of nucleus pulposus cells under tumour necrosis factor alpha stimulation.

OBJECTIVES: Tumour necrosis factor alpha (TNF-α) expressed by nucleus pulposus cells (NPCs) plays a critical role in intervertebral disc (IVD) degeneration. A key unfolded protein response (UPR) component, X-box binding protein 1 (XBP1) and nuclear factor-kappa B (NF-κB) are essential for cell survival and proliferation. The aim of our study was to elucidate the roles of XBP1 and NF-κB in IVD degeneration (IDD). MATERIALS AND METHODS: Rat NPCs were cultured with TNF-α in the presence or absence of XBP1 and NF-κB-p65 small interfering RNA. The associated genes and proteins were evaluated through quantitative real-time PCR, Western blot analyses and immunofluorescence staining to monitor UPR and NF-κB signalling and identify the regulatory mechanism of p65 by XBP1. Cell counting kit-8 assay, cell cycle analysis and related gene and protein expression were performed to examine the proliferation of NPCs. RESULTS: The acute exposure of TNF-α accelerated the proliferation of rat NPCs by activating the UPR/XBP1 pathway. XBP1 signalling favoured the phosphorylation and nuclear translocation of p65 subunit of NF-κB. The activation of NF-κB in the later phase also enhanced NPC proliferation. CONCLUSIONS: Unfolded protein response reinforces the survival and proliferation of NPCs under TNF-α stimulation by activating the XBP1 pathway, and NF-κB serves as a vital mediator in these events. The XBP1 signalling of UPR can be a novel therapeutic target in IDD.

Comparison of percutaneous endoscopic lumbar discectomy versus microendoscopic discectomy for the treatment of lumbar disc herniation: a meta-analysis.

PURPOSE: We conducted a systematic review and meta-analysis to compare the clinical outcomes of percutaneous endoscopic lumbar discectomy (PELD) and microendoscopic discectomy (MED) for the treatment of lumbar disc herniation (LDH), and to clarify whether PELD is more superior to MED. METHODS: We performed a comprehensive search in the databases of MEDLINE, EMBASE, PubMed, Web of Science, Cochrane database, CNKI, and Wanfang Data to acquire all relevant studies up to July 2018. The searched literatures were then screened according to the strict inclusion and exclusion criteria. The critical data were extracted and analyzed utilizing Review Manager software. The pooled effects were calculated by mean difference (MD) or odds ratio (OR) with 95% confidence intervals (CI) on the basis of data attributes. RESULTS: A total of 18 studies (2161 patients, 1093 in the PELD group and 1068 in the MED group) were included in this systematic review and meta-analysis. At last follow-up, the results revealed that no significant difference was found between PELD group and MED group with respect to ODI (MD - 0.30; 95% CI - 1.02 to 0.42; P = 0.41), VAS-leg pain (MD - 0.18; 95% CI - 0.45 to 0.09; P = 0.19), VAS-unspecified (MD - 0.00; 95% CI - 0.05 to 0.04; P = 0.94), excellent & good rate (OR, 1.04; 95% CI 0.68 to 1.59; P = 0.86), total complication rate (OR, 0.96; 95% CI 0.65 to 1.43; P = 0.85), dural tear rate (OR, 0.39; 95% CI 0.10 to 1.55; P = 0.18), and residue or recurrence rate (OR, 2.22; 95% CI 1.02 to 4.83; P = 0.05). When compared to MED group, the PELD group showed significantly better results with regard to shorter length of incision (MD - 1.18; 95% CI - 1.39 to - 0.97; P < 0.00001), less blood loss (MD - 45.17; 95% CI - 64.74 to - 25.60; P < 0.00001), shorter post-operative in-bed time (MD - 59.11; 95% CI - 71.19 to - 47.04; P < 0.00001), shorter post-operative hospital stay (MD - 3.07; 95% CI - 4.81 to - 1.33; P < 0.00001), shorter total hospital stay (MD - 2.29; 95% CI - 3.03 to - 1.55; P < 0.00001), and lower VAS-back pain at last follow-up (MD - 0.77; 95% CI - 1.31 to - 0.24; P = 0.005), but with significantly worse results such as more fluoroscopy (MD 7.63; 95% CI 5.25 to 10.01; P < 0.00001) and higher re-operation rate (OR, 2.67; 95% CI 1.07 to 6.67; P = 0.04). Although no significant difference was found between the two groups in terms of duration of operation (MD 6.27; 95% CI - 2.44 to 14.98; P = 0.16) and total hospital cost (MD - 0.69; 95% CI - 12.60 to 11.23; P = 0.91), further subgroup analysis revealed that the duration of operation was significantly longer in the PELD group compared with the MED group in "Years before 2016" (MD 24.97; 95% CI 7.07 to 42.87; P = 0.006) and "Year 2016 to 2017" (MD 6.57; 95% CI 0.58 to 12.55; P = 0.03) subgroups but not in the subgroup "Year 2018" (MD - 5.66; 95% CI - 18.84 to 7.53; P = 0.40), and that the total hospital cost was significantly more in the PELD group compared with the MED group in the subgroup "Southeast of China" (MD 6.67; 95% CI 3.23 to 10.28; P = 0.0002) but not in the subgroup "Midwest of China" (MD - 8.09; 95% CI - 17.99 to 1.80; P = 0.11). CONCLUSIONS: For the treatment of LDH, both of PELD and MED can reach excellent results and no superiority was found between the two minimally invasive procedures with regard to duration of operation, ODI, VAS-leg pain, VAS-unspecified, excellent & good rate, total complication rate, dural tear rate, and residue or recurrence rate. While PELD can achieve better outcomes with respect to the length of incision, blood loss, post-operative in-bed time, post-operative hospital stay, total hospital stay, and VAS-back pain at last follow-up, however, MED showed certain advantages of less fluoroscopic times and lower re-operation rate. More practice and development are needed to make up for the deficiencies of PELD. Besides, the economic factor should also be considered according to different regions before making the treatment strategies. Well-defined randomized controlled trials with large samples are needed to further confirm these results.

Protein kinase RNA-like ER kinase/eukaryotic translation initiation factor 2α pathway attenuates tumor necrosis factor alpha-induced apoptosis in nucleus pulposus cells by activating autophagy.

Cellular loss induced by tumor necrosis factor alpha (TNF-α) contributes to the pathogenesis of intervertebral disc (IVD) degeneration. Cellular stress induced by TNF-α activates several processes to restore cell homeostasis. These processes include autophagy, endoplasmic reticulum stress, and related unfolded protein response (UPR). However, the effect and mechanism of UPR and autophagy regulated by TNF-α in IVD degeneration (IDD) remain unclear. The effect of autophagy on biological changes in nucleus pulposus cells (NPCs) also remains elusive. In this study, rat NPCs were cultured with TNF-α in the presence or absence of the UPR or autophagy pathway small-interfering RNAs. The associated genes and proteins were evaluated through immunofluorescence staining, quantitative real-time polymerase chain reaction (qRT-PCR) and western blot analyses to monitor UPR and autophagy signaling and identify the regulatory mechanism of autophagy by the UPR pathway. Trypan blue exclusion assay, cell flow cytometry, terminal deoxynucleotidyl transferase dUTP nick end labeling staining, qRT-PCR, and western blot analyses were performed to examine the apoptosis of NPCs. The results showed that the acute exposure of TNF-α induced the apoptosis of rat NPCs and activated the protein kinase RNA-like ER kinase/eukaryotic translation initiation factor 2α (PERK/eIF2α) pathway of UPR and initiated autophagy. Silencing the PERK/eIF2α pathway or inhibiting autophagy enhanced the apoptosis of NPCs. Interference of the PERK/eIF2α pathway suppressed the autophagy of rat NPCs under TNF-α stimulation. Taken together, the PERK/eIF2α pathway reinforces the survival of NPCs under TNF-α stimulation by activating autophagy. Therefore, PERK/eIF2α-dependent autophagy could be a novel biological therapeutic target for IDD.

Acid-Sensing Ion Channel 1a Regulates Fate of Rat Nucleus Pulposus Cells in Acid Stimulus Through Endoplasmic Reticulum Stress.

Acid-sensing ion channel 1a (ASIC1a) participates in human intervertebral disc degeneration (IVDD) and regulates the destiny of nucleus pulposus cells (NPCs) in acid stimulus. However, the mechanism of ASIC1a activation and its downstream pathway remain unclear. Endoplasmic reticulum (ER) stress also participates in the acid-induced apoptosis of NPCs. The main purpose of this study was to investigate whether there is any connection between ASIC1a and ER stress in an acid-induced nucleus pulposus degeneration model. The IVDs of Sprague-Dawley rats were stained by immunohistochemical staining to evaluate the expression of ASIC1a in normal and degenerated rat nucleus pulposus. ASIC1a expression was also quantified by quantitative real-time-polymerase chain reaction and Western blotting analysis. NPCs were exposed to the culture media with acidity at pH 7.2 and 6.5 for 24 h, with or without 4-phenylbutyrate (4-PBA, a blocker of the ER stress pathway). Cell apoptosis was examined by Annexin V/Propidium Iodide (PI) staining and was quantified using flow cytometry analysis. ASIC1a-mediated intracellular calcium was determined by Ca2+ imaging using Fura-2-AM. Acidity-induced changes in ER stress markers were studied using Western blotting analysis. In vivo, ASIC1a expression was upregulated in natural degeneration. In vitro, acid stimulus increased intracellular calcium levels, but this effect was blocked by knockdown of ASIC1a, and this reversal was partly inhibited by 4-PBA. In addition, blockade of ASIC1a reduced expression of ER stress markers, especially the proapoptotic markers. ASIC1a partly regulates ER stress and promotes apoptosis of NPCs under acid stimulus and may be a novel therapeutic target in IVDD.

Endoplasmic Reticulum Stress Facilitates the Survival and Proliferation of Nucleus Pulposus Cells in TNF-α Stimulus by Activating Unfolded Protein Response.

Intervertebral disc (IVD) degeneration is closely related to inflammatory cytokines, such as tumor necrosis factor alpha (TNF-α). The endoplasmic reticulum (ER) serves several important cell functions, which are essential for normal cell metabolism and survival. This study aims to clarify the role of ER stress and unfolded protein response (UPR) in TNF-α-induced biological changes in rat nucleus pulposus cells (NPCs) and IVD degeneration. In our research, rat NPCs were cultured with different concentrations of TNF-α in the presence or absence of ER stress inhibitors. Related genes and proteins were measured by immunofluorescence staining, quantitative real-time PCR, and Western blot analyses to monitor ER stress. Cell proliferation was evaluated by CCK-8 assay and cyclin D1 expression. Apoptosis was detected by flow cytometry and Western blot analyses. Our results showed that TNF-α induced the apoptosis of some NPCs in the early stage and then accelerated the proliferation of surviving cells. In addition, TNF-α stimulus upregulated ER stress markers and initiated UPR. However, these effects could be reversed by inhibitors, thereby reducing cell proliferation and enhancing apoptosis. In conclusion, ER stress reinforces the survival and proliferation of NPCs in TNF-α stimulus by activating UPR signaling, which could be an important therapeutic target in the future.

Formation, function, and exhaustion of notochordal cytoplasmic vacuoles within intervertebral disc: current understanding and speculation.

Notochord nucleus pulposus cells are characteristic of containing abundant and giant cytoplasmic vacuoles. This review explores the embryonic formation, biological function, and postnatal exhaustion of notochord vacuoles, aiming to characterize the signal network transforming the vacuolated nucleus pulposus cells into the vacuole-less chondrocytic cells. Embryonically, the cytoplasmic vacuoles within vertebrate notochord originate from an evolutionarily conserved vacuolation process during neurulation, which may continue to provide mechanical and signal support in constructing a mammalian intervertebral disc. For full vacuolation, a vacuolating specification from dorsal organizer cells, synchronized convergent extension, well-structured notochord sheath, and sufficient post-Golgi trafficking in notochord cells are required. Postnatally, age-related and species-specific exhaustion of vacuolated nucleus pulposus cells could be potentiated by Fas- and Fas ligand-induced apoptosis, intolerance to mechanical stress and nutrient deficiency, vacuole-mediated proliferation check, and gradual de-vacuolation within the avascular and compression-loaded intervertebral disc. These results suggest that the notochord vacuoles are active and versatile organelles for both embryonic notochord and postnatal nucleus pulposus, and may provide novel information on intervertebral disc degeneration to guide cell-based regeneration.

Endoplasmic Reticulum Stress Is Involved in Nucleus Pulposus Degeneration and Attenuates Low pH-Induced Apoptosis of Rat Nucleus Pulposus Cells.

The microenvironment of degenerative intervertebral disk (IVD) is characteristic of a high concentration of lactic acid and low pH levels, whereas the underlying mechanism has not been clearly defined. Endoplasmic reticulum (ER) is the hub of interactions between environmental signals and cellular biological functions, the malfunction of which is closely involved in the pathogenesis of multiple disorders, including IVD degeneration (IVDD). This research mainly aims at exploring what role ER stress plays in the natural process of IVDD and pH-induced apoptosis of rat nucleus pulposus (NP) cells (NPCs). The IVD of Sprague-Dawley rats at different ages was stained by Hematoxylin-Eosin staining to visualize the histocytological changes during the nature process of IVDD. Immunohistochemical staining was performed to evaluate the expression of ER stress markers within normal and degenerated NP. The ER stress markers were also quantified by quantitative real-time-polymerase chain reaction (PCR) and Western blotting analysis, respectively. NPCs were exposed to the culturing media with acidity of pH 7.4, 7.0, 6.5, or 6.0 for 24-72 h, with or without the supplement of 4-phenylbutyrayte (4-PBA, the blocker of ER stress pathways). Changes in cell viability were evaluated by CCK-8 assay and neutral red assay, whereas apoptosis was stained by Annexin-V/PI staining and quantified by flow cytometry analysis. The acidity-induced changes in the expression of ER stress markers were studied by immunofluorescent staining, qRT-PCR, and Western blotting analysis. In vivo, the expression of GRP78 and XBP1 was downregulated whereas CHOP and Caspase12 were upregulated in natural degeneration. In vitro, low pH induced apoptosis of rat NPCs; prolonged exposure of acid reduced cell viability and caused upregulation of ER stress markers. 4-PBA was used to alleviate ER stress, and it promoted acid-induced apoptosis of NPCs. ER stress is involved in NP natural degeneration and attenuates low-pH-induced apoptosis of NPCs.

Tumor necrosis factor α modulates sodium-activated potassium channel SLICK in rat dorsal horn neurons via p38 MAPK activation pathway.

The dorsal horn (DH) of the spinal cord is the integrative center that processes and transmits pain sensation. Abnormal changes in ion channel expression can enhance the excitability of pain-related DH neurons. Sodium-activated potassium (KNa) channels are highly expressed particularly in the central nervous system; however, information about whether rat DH neurons express the SLICK channel protein is lacking, and the direct effects on SLICK in response to inflammation and the potential signaling pathway mediating such effects are yet to be elucidated. Here, using cultured DH neurons, we have shown that tumor necrosis factor-α inhibits the total outward potassium current IK and the KNa current predominantly as well as induces a progressive loss of firing accommodation. However, we found that this change in channel activity is offset by the p38 inhibitor SB202190, thereby suggesting the modulation of SLICK channel activity via the p38 MAPK pathway. Furthermore, we have demonstrated that the tumor necrosis factor-α modulation of KNa channels does not occur at the level of SLICK channel gating but arises from possible posttranslational modification.

Acid-sensing ion channel 1a regulates the survival of nucleus pulposus cells in the acidic environment of degenerated intervertebral discs.

OBJECTIVES: Activation of acid-sensing ion channel 1a (ASIC1a) is responsible for tissue injury caused by acidosis in nervous systems. But its physiological and pathological roles in nucleus pulposus cells (NPCs) are unclear. The aim of this study is to investigate whether ASIC1a regulates the survival of NPCs in the acidic environment of degenerated discs. MATERIALS AND METHODS: NPCs were isolated and cultured followed by immunofluorescent staining and Western-blot analysis for ASIC1a. Intracellular calcium ([Ca2+]i) was determined by Ca2+-imaging using Fura-2-AM. Cell necrosis, apoptosis, and senescence following acid exposure were determined using lactate dehydrogenase (LDH) release assay, annexin V-fluorescein isothiocyanate/propidium iodide dual-staining and cell cycle analysis, respectively, followed by Western-blot analysis for apoptosis-related proteins (Bax, Bcl-2, and caspase-3) and senescence-related proteins (p53, p21, and p16). Effects of treatment with psalmotoxin-1 (PcTX1, blocker of ASIC1a) on [Ca2+]i and cell survival were investigated. RESULTS: ASIC1a was detected in healthy NPCs, and its expression was significantly higher in degenerated cells. When NPCs were treated with PcTX1, acid-induced increases in [Ca2+]i were significantly inhibited. PcTX1 treatment also resulted in decreased LDH release, cell apoptosis and cell cycle arrest in acid condition. Acid exposure decreased the expression of Bcl-2 and increased the expression of Bax, cleaved caspase-3 and senescence-related proteins (p53, p21, and p16), which was inhibited by PcTX1. CONCLUSION: The present findings suggest that further understanding of ASIC1a functionality may provide not only a novel insight into intervertebral disc biology but also a novel therapeutic target for intervertebral disc degeneration.