Effect of nutrient deprivation on the viability of intervertebral disc cells

Different effects of abnormal mechanical stress on temporomandibular joint cartilage, subchondral bone, and discs

Background

Temporomandibular joint disorder (TMJD) is a group of diseases occurring in the temporomandibular joint (TMJ) with clinical manifestations of pain in the joint area, mastication disorders, and restriction of mouth opening, which is one of the most common diseases of the oral and maxillofacial region, and its specific etiology has not yet been fully elucidated. As a biomechanical orchestrator, the TMJ mediates dynamic transduction of masticatory forces during the functional loading cycle. Notably, as a secondary cartilage type, the condylar cartilage exhibits postnatal remodeling that is critically dependent on functional mechanical stimulation. Abnormal mechanical stimulation can result in structural dysfunction of the TMJ.

Objective

The purpose of this review was to outline the remodeling responses of TMJ cartilage, subchondral bone, and disc to abnormal mechanical stimulation of different types and intensities, especially the subchondral bone and articular disc.

Conclusion

Abnormal mechanical stress induces degeneration of the condylar cartilage, characterized by dysregulated chondrocyte proliferation and differentiation, elevated cell apoptosis, and ECM injury. The ability of TMJ condylar cartilage to adapt to changes in the mechanical load environment for remodeling is influenced by age, as well as the type, intensity, and duration of the applied mechanical load. Bone loss is often the first response of subchondral bone to abnormal mechanical forces. Abnormal mechanical stimuli affect nutrient supply and matrix metabolism of TMJ discs.

Piezo1 exacerbates inflammation-induced cartilaginous endplate degeneration by activating mitochondrial fission via the Ca2+/CaMKII/Drp1 axis

Mitochondrial homeostasis plays a crucial role in degenerative joint diseases, including cartilaginous endplate (CEP) degeneration. To date, research into mitochondrial dynamics in IVDD is at an early stage. Since Piezo1 is a novel Ca2+-permeable channel, we asked whether Piezo1 could modulate mitochondrial fission through Ca2+ signalling during CEP degeneration. In vitro and in vivo models of inflammation-induced CEP degeneration were established with lipopolysaccharide (LPS). We found increased expression of Piezo1 in degenerated CEP tissues and LPS-treated CEP cells. The Piezo1 activator Yoda1 exacerbated CEP cell senescence and apoptosis by triggering Ca2+ influx. Yoda1 also induced mitochondrial fragmentation and dysfunction. In contrast, the Piezo1 inhibitor GsMTx4 exerted cytoprotective effects in LPS-treated CEP cells. Additionally, the CaMKII inhibitor KN-93 reversed Yoda1-induced mitochondrial fission and restored mitochondrial function. Mechanistically, the phosphorylation and mitochondrial translocation of Drp1 were regulated by the Ca2+/CaMKII signalling. The Drp1 inhibitor Mdivi-1 suppressed mitochondrial fission, then reduced mitochondrial dysfunction and CEP cell death. Moreover, knockdown of Piezo1 by siRNA hindered CaMKII and Drp1 activation, facilitating the redistribution of mitochondrial Drp1 to the cytosol in LPS-treated CEP cells. Piezo1 silencing improved mitochondrial morphology and function, thereby rescuing CEP cell senescence and apoptosis under inflammatory conditions. Finally, subendplate injection of GsMTx4 or AAV-shPiezo1 alleviated CEP degeneration in a rat model. Thus, Piezo1 may exacerbate inflammation-induced CEP degeneration by triggering mitochondrial fission and dysfunction via the Ca2+/CaMKII/Drp1 axis.

The role of loading-induced convection versus diffusion on the transport of small molecules into the intervertebral disc

PURPOSE

Limited nutrient transport is hypothesized to be involved in intervertebral disc (IVD) degeneration. It is widely recognized that the dominant mode of transport of small molecules such as glucose is via diffusion, rather than convection. However, recent findings suggest a role for convection-induced by fast (motion-related) and slow (diurnal) dynamic loading in molecular transport of even such small solutes. The aim of this study was to investigate whether fluid exchange induced by simulated physiological loading (composed of both fast cyclic or slower diurnal loading) can influence the molecular transport of a small molecule through the cartilage endplate (CEP) into the nucleus pulposus (NP) of IVDs.

METHODS

The molecular transport of fluorescein through the CEP and into the NP was studied in a bovine CEP/NP explant model and loading was applied by an axial compression bioreactor. The loaded explants (convection and diffusion) were compared to unloaded explants (diffusion alone).

RESULTS

In the initial 24 h, there were no differences between loaded and unloaded explants, indicating that convection did not enhance molecular transport of small solutes over diffusion alone. Notably, after 48 h which corresponds to two complete diurnal cycles of tissue compression, fluid exudation/imbibing and redistribution, the fluorescein concentration was significantly increased in the top and bottom layer of the explant, when compared to the unloaded explant.

CONCLUSIONS

Slower diurnal cyclic compression of the IVD might enhance the transport of small molecules into the IVD although it could not be discerned whether this was due to diffusion/convection or a combination.

Role of Magnetic Resonance Spectroscopy and T2 Relaxometry as Imaging Biomarker of Early Lumbar Intervertebral Disc Degeneration

STUDY DESIGN

Observational comparative study.

OBJECTIVE

To study the role of magnetic resonance spectroscopy (MRS) and T2 relaxometry (T2r) as imaging biomarkers for identifying early lumbar disc degeneration.

METHODS

We evaluated 236 discs in normal volunteers and 215 discs in low back pain (LBP) patients by MRS and T2r to document the molecular spectra of various metabolites as well as disc hydration and collagen content, respectively. All volunteer discs were Pfirrmann grade 1 (PF1), whereas patients with LBP had PF 1 (n = 156) and PF 2 (n = 59). The study population was compared in three age groups: A (20-30 years), B (30-40 years), and C (40-50 years).

RESULTS

T2r, an indicator of collagen and hydration, was higher in volunteers (121.8 ± 31.1), compared to PF 1 patients (110.68 ± 23.96) and PF 2 patients (90.15 ± 25.81) (P = 0.001). Proteoglycan assessed by MRS was more stable for volunteers (3.39 ± 1.69) and PF 1 patients (3.6 ± 1.69) but reduced in PF 2 patients (2.86 ± 1.47), showing that structural molecules did not alter within the PF 1. However, lactate and other metabolites showed a difference even within PF1 between volunteers and LBP patients. We were able to identify a unique subset of PF 1 that had a normal value of proteoglycan and T2r but altered metabolite distribution, which may represent early disc degeneration (DD).

CONCLUSION

MRS and T2r can be used as imaging biomarkers for early DD by identifying altered metabolic activity with an intact matrix.

pH: A major player in degenerative intervertebral disks

Chronic lower back pain is the leading cause of disability worldwide, generating a socioeconomic cost of over $100 billion annually in the United States. Among the prominent causes of low back pain (LBP) is degeneration of the intervertebral disk (IVD), a condition known as degenerative disk disease (DDD). Despite the prevalence of DDD and multiple studies demonstrating its relationship with LBP, the mechanisms by which it contributes to pain remain unknown. Previous studies have identified potential causes for this pain, such as extracellular matrix (ECM) breakdown, changes in biomechanics, and pro-inflammatory signals. Possible pain treatments targeting these factors have been developed but with limited effects. However, low pH in DDD is a potential pain generator whose role has largely been unexplored and underappreciated. This review highlights hyperacidity's effects on the IVD, such as catabolism of disk cells and ECM, neoinnervation, altered mechanical signaling, and expression of pro-inflammatory cytokines and ion channels. This review aims to discuss what is known about the contributions of acidity to DDD pain, identify the knowledge gaps on this topic, and propose what research can be conducted to fill these gaps. We must better understand the underlying mechanisms of DDD and the interaction between hyperacidity and nociception to develop better therapeutics for this disease.

Development and characterization of antacid microcapsules to buffer the acidic intervertebral disc microenvironment

During intervertebral disc (IVD) degeneration, microenvironmental challenges such as decreasing levels of glucose, oxygen, and pH play crucial roles in cell survival and matrix turnover. Antacids, such as Mg(OH)2 and CaCO3, entrapped in microcapsules are capable of neutralizing acidic microenvironments in a controlled fashion and therefore may offer the potential to improve the acidic niche of the degenerated IVD and enhance cell-based regeneration strategies. The objectives of this work were, first, to develop and characterize antacid microcapsules and assess their neutralization capacity in an acidic microenvironment and, second, to combine antacid microcapsules with cellular microcapsules in a hybrid gel system to investigate their neutralization effect as a potential therapeutic in a disc explant model. To achieve this, we screened five different pH- neutralizing agents (Al(OH)3, Mg(OH)2, CaCO3, and HEPES) in terms of their pH neutralization capacities, with Mg(OH)2 or CaCO3 being carried forward for further investigation. Antacid-alginate microcapsules were formed at different concentrations using the electrohydrodynamic spraying process and assessed in terms of size, buffering kinetics, cell compatibility, and cytotoxicity. Finally, the combination of cellular microcapsules and antacid capsules was examined in a bovine disc explant model under physiological degenerative conditions. Overall, CaCO3 was found to be superior in terms of neutralization capacities, release kinetics, and cellular response. Specifically, CaCO3 elevated the acidic pH to neutral levels and is estimated to be maintained for several weeks based on Ca2+ release. Using a disc explant model, it was demonstrated that CaCO3 microcapsules were capable of increasing the local pH within the core of a hybrid cellular gel system. This work highlights the potential of antacid microcapsules to positively alter the challenging acidic microenvironment conditions typically observed in degenerative disc disease, which may be used in conjunction with cell therapies to augment regeneration.

Glucose deprivation-induced disulfidptosis in human nucleus pulposus cells: a novel pathological mechanism of intervertebral disc degeneration

BACKGROUND

Limited supply of certain nutrients and deregulation of nucleus pulposus (NP) plays a key role in the pathogenesis of intervertebral disc degeneration (IVDD). However, whether nutrient deprivation-induced cell death, particularly disulfidptosis, contributes to the depletion of NP cells and the development of IVDD, is unknown.

METHODS

RNA-seq, single-cell RNA-seq, and Genome-wide DNA methylation datasets of nucleus pulposus tissue were collected for bioinformatic analysis. Predictive models of disulfidptosis related genes in IVDD were constructed by machine learning and their differential expression was analyzed. In addition, we performed cell subsets identification analysis, cell-cell communications analysis, and functional enrichment analysis of key genes in the core subset based on single-cell RNA-seq data of NP tissues isolated from one normal sample and one IVDD sample. Finally, glucose deprivation-induced disulfidptosis in human NP cells (HNPCs) was verified by various cell death inhibitors and disulfidptosis-related molecular markers.

RESULTS

We found the disulfidptosis signal was significantly activated in the IVDD group. Using single-cell RNA-seq analysis, we focused on the chondrocytes and found that disulfidptosis-related genes significantly highly expressed in the IVDD C4 chondrocyte subset, which was identified as a new disulfidptosis-associated cell subset. Correlation analysis revealed the negative correlation between SLC7A11 (driving gene of disulfidptosis) and the glucose transporter GLUTs (SLC2A1-4) family genes (suppressing genes of disulfidptosis) in the IVDD group. We also found obvious cell death in HNPC upon glucose starvation, while employment of various cell death inhibitors could not inhibit glucose starvation-induced death in HNPCs. Moreover, the accumulation of disulfide bonds in cytoskeletal proteins was indicated by slowed migration in non-reducible protein blotting experiments. 2-DG, a key disulfidptosis inhibitor, significantly rescued cell death caused by glucose starvation through lowering the NADP+/NADPH ratio.

CONCLUSIONS

We validated the occurrence of disulfidptosis in HPNCs and identified a novel disulfidptosis-associated cell subset, followed by experimental verification of disulfidptosis in a glucose-limited context to mimic a fall in nutrient supply during the development disc degeneration. These findings provided new insights into the pathological mechanisms of IVDD and encourage us to explore potential therapeutic targets involved in the regulation of disulfidptosis for the prevention of intervertebral disc degeneration.

Diverse and multifunctional roles for perlecan (HSPG2) in repair of the intervertebral disc

Perlecan is a widely distributed, modular, and multifunctional heparan sulfate proteoglycan, which facilitates cellular communication with the extracellular environment to promote tissue development, tissue homeostasis, and optimization of biomechanical tissue functions. Perlecan-mediated osmotic mechanotransduction serves to regulate the metabolic activity of cells in tissues subjected to tension, compression, or shear. Perlecan interacts with a vast array of extracellular matrix (ECM) proteins through which it stabilizes tissues and regulates the proliferation or differentiation of resident cell populations. Here we examine the roles of the HS-proteoglycan perlecan in the normal and destabilized intervertebral disc. The intervertebral disc cell has evolved to survive in a hostile weight bearing, acidic, low oxygen tension, and low nutrition environment, and perlecan provides cytoprotection, shields disc cells from excessive compressive forces, and sequesters a range of growth factors in the disc cell environment where they aid in cellular survival, proliferation, and differentiation. The cells in mechanically destabilized connective tissues attempt to re-establish optimal tissue composition and tissue functional properties by changing the properties of their ECM, in the process of chondroid metaplasia. We explore the possibility that perlecan assists in these cell-mediated tissue remodeling responses by regulating disc cell anabolism. Perlecan's mechano-osmotic transductive property may be of potential therapeutic application.

In silico modeling the potential clinical effect of growth factor treatment on the metabolism of human nucleus pulposus cells

Background

While growth factors have the potential to halt degeneration and decrease inflammation in animal models, the literature investigating the effect of dosage on human cells is lacking. Moreover, despite the completion of clinical trials using growth differentiation factor-5 (GDF-5), no results have been publicly released.

Aims

The overall objective was to quantitatively assess the effect of three clinically relevant concentrations of GDF-5 (0.25, 1, and 2 mg) as a therapeutic for disc regeneration.

Materials and methods

Firstly, this work experimentally determined the effects of GDF-5 concentration on the metabolic and matrix synthesis rates of human nucleus pulposus (NP) cells. Secondly, in silico modeling was employed to predict the subsequent regenerative effect of different GDF-5 treatments (± cells).

Results

This study suggests a trend of increased matrix synthesis with 0.25 and 1 mg of GDF-5. However, 2 mg of GDF-5 significantly upregulates oxygen consumption. Despite this, in silico models highlight the potential of growth factors in promoting matrix synthesis compared to cell-only treatments, without significantly perturbing the nutrient microenvironment.

Discussion

This work elucidates the potential of GDF-5 on human NP cells. Although the results did not reveal statistical differences across all doses, the variability and response among donors is an interesting finding. It highlights the complexity of human response to biological treatments and reinforces the need for further human research and personalized approaches. Furthermore, this study raises a crucial question about whether these potential biologics are more regenerative in nature or better suited as prophylactic therapies for younger patient groups.

Conclusion

Biological agents exhibit unique characteristics and features, demanding tailored development strategies and individualized assessments rather than a one-size-fits-all approach. Therefore, the journey to realizing the full potential of biological therapies is long and costly. Nonetheless, it holds the promise of revolutionizing spinal healthcare and improving the quality of life for patients suffering from discogenic back pain.

Chronic Low Back Pain: History, Symptoms, Pain Mechanisms, and Treatment

Chronic low back pain (cLBP) is the most frequently reported cause of years lived with disability. Identifying the anatomical structures or dysfunction contributing to patients' symptoms is critical to guiding treatment. The etiology of back pain and differential diagnosis is often broad, ranging from non-degenerative cLBP (trauma, tumor, inflammation, infection, etc.) to degenerative (also described as nonspecific) cLBP. After eliminating suspicion for more insidious causes of cLBP, a thorough investigation can be conducted in an attempt to identify a source of degenerative cLBP. Degenerative cLBP can originate from many sources, and a detailed understanding of the structures potentially involved is invaluable for an accurate diagnosis. This review article aims to provide a broad overview of the utility of clinical history, physical exam findings, imaging findings, and diagnostic procedures in identifying the cause of patients' cLBP. We provide a framework to help guide clinicians by dividing the structures into groups as follows: anterior vertebral column, posterior vertebral column, and extra-vertebral pain. For each condition listed, we touch on the treatment options that can be considered.

Glucose depletion decreases cell viability without triggering degenerative changes in a physiological nucleus pulposus explant model

Although the etiology of intervertebral disc degeneration is still unresolved, the nutrient paucity resulting from its avascular nature is suspected of triggering degenerative processes in its core: the nucleus pulposus (NP). While severe hypoxia has no significant effects on NP cells, the impact of glucose depletion, such as found in degenerated discs (0.2-1 mM), is still uncertain. Using a pertinent ex-vivo model representative of the unique disc microenvironment, the present study aimed, therefore, at determining the effects of "degenerated" (0.3 mM) glucose levels on bovine NP explant homeostasis. The effects of glucose depletion were evaluated on NP cell viability, apoptosis, phenotype, metabolism, senescence, extracellular matrix anabolism and catabolism, and inflammatory mediator production using fluorescent staining, RT-qPCR, (immuno)histology, ELISA, biochemical, and enzymatic assays. Compared to the "healthy" (2 mM) glucose condition, exposure to the degenerated glucose condition led to a rapid and extensive decrease in NP cell viability associated with increased apoptosis. Although the aggrecan and collagen-II gene expression was also downregulated, NP cell phenotype, and senescence, matrix catabolism, and inflammatory mediator production were not, or only slightly, affected by glucose depletion. The present study provided evidence for glucose depletion as an essential player in NP cell viability but also suggested that other microenvironment factor(s) may be involved in triggering the typical shift of NP cell phenotype observed during disc degeneration. The present study contributes new information for better understanding disc degeneration at the cellular-molecular levels and thus helps to develop relevant therapeutical strategies to counteract it.

ISSLS prize in clinical/bioengineering science 2024: How standing and supine positions influence nutrient transport in human lumbar discs?-A serial post-contrast MRI study evaluating interplay between convection and diffusion

PURPOSE

The intervertebral disc being avascular depends on diffusion and load-based convection for essential nutrient supply and waste removal. There are no reliable methods to simultaneously investigate them in humans under natural loads. For the first time, present study aims to investigate this by strategically employing positional MRI and post-contrast studies in three physiological positions: supine, standing and post-standing recovery.

METHODS

A total of 100 healthy intervertebral discs from 20 volunteers were subjected to a serial post-contrast MR study after injecting 0.3 mmol/kg gadodiamide and T1-weighted MR images were obtained at 0, 2, 6, 12 and 24 h. At each time interval, images were obtained in three positions, i.e. supine, standing and post-standing recovery supine. The signal intensity values at endplate zone and nucleus pulposus were measured. Enhancement percentages were calculated and analysed comparing three positions.

RESULTS

During unloaded supine position, there was slow gradual increase in enhancement reaching peak at 6 h. When the subjects assumed standing position, there was immediate loss of enhancement at nucleus pulposus which resulted in reciprocal increase in enhancement at endplate zone (washout phenomenon). Interestingly, when subjects assumed the post-standing recovery position, the nucleus pulposus regained the enhancement and endplate zone showed reciprocal loss (pumping-in phenomenon).

CONCLUSIONS

For the first time, present study documented acute effects of physiological loading and unloading on nutrition of human discs in vivo. While during rest, solutes diffused gradually into disc, the diurnal short loading and unloading redistribute small solutes by convection. Standing caused rapid solute depletion but promptly regained by assuming resting supine position.

Bioenergetic dysfunction in the pathogenesis of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is a frequent cause of low back pain and is the most common cause of disability. Treatments for symptomatic IVD degeneration, including conservative treatments such as analgesics, physical therapy, anti-inflammatories and surgeries, are aimed at alleviating neurological symptoms. However, there are no effective treatments to prevent or delay IVD degeneration. Previous studies have identified risk factors for IVD degeneration such as aging, inflammation, genetic factors, mechanical overload, nutrient deprivation and smoking, but metabolic dysfunction has not been highlighted. IVDs are the largest avascular structures in the human body and determine the hypoxic and glycolytic features of nucleus pulposus (NP) cells. Accumulating evidence has demonstrated that intracellular metabolic dysfunction is associated with IVD degeneration, but a comprehensive review is lacking. Here, by reviewing the physiological features of IVDs, pathological processes and metabolic changes associated with IVD degeneration and the functions of metabolic genes in IVDs, we highlight that glycolytic pathway and intact mitochondrial function are essential for IVD homeostasis. In degenerated NPs, glycolysis and mitochondrial function are downregulated. Boosting glycolysis such as HIF1α overexpression protects against IVD degeneration. Moreover, the correlations between metabolic diseases such as diabetes, obesity and IVD degeneration and their underlying molecular mechanisms are discussed. Hyperglycemia in diabetic diseases leads to cell senescence, the senescence-associated phenotype (SASP), apoptosis and catabolism of extracellualr matrix in IVDs. Correcting the global metabolic disorders such as insulin or GLP-1 receptor agonist administration is beneficial for diabetes associated IVD degeneration. Overall, we summarized the recent progress of investigations on metabolic contributions to IVD degeneration and provide a new perspective that correcting metabolic dysfunction may be beneficial for treating IVD degeneration.

Biological Therapeutic Modalities for Intervertebral Disc Diseases: An Orthoregeneration Network (ON) Foundation Review

Orthoregeneration is defined as a solution for orthopaedic conditions that harnesses the benefits of biology to improve healing, reduce pain, improve function, and, optimally, provide an environment for tissue regeneration. Options include drugs, surgical intervention, scaffolds, biologics as a product of cells, and physical and electromagnetic stimuli. The goal of regenerative medicine is to enhance the healing of tissue after musculoskeletal injuries as both isolated treatment and adjunct to surgical management, using novel therapies to improve recovery and outcomes. Various orthopaedic biologics (orthobiologics) have been investigated for the treatment of pathology involving the spine, including lower back pain, with or without numbness and/or dysfunction in the lower extremities, disc herniation, spinal stenosis, and spondylolisthesis. Promising and established treatment modalities include repair of the annulus fibrosis, injection of expanded or nonexpanded autologous or allogenic cells that are chondrogenic or from a stem cell lineage used to promote matrix tissue regeneration of the intervertebral disc, including nucleus pulpous cells and mesenchymal stem cells isolated from bone marrow, umbilical cord blood, or adipose tissue; and injection of platelet-rich plasma, platelet-rich fibrin, or fibrin sealant. Early clinical studies show promise for pain reduction and functional recovery. LEVEL OF EVIDENCE: Level V, expert opinion.

Imaging of Discogenic and Vertebrogenic Pain

Chronic low back pain is a major source of pain and disability globally involving multifactorial causes. Historically, intervertebral disc degeneration and disruption have been associated as primary back pain triggers of the anterior column, termed "discogenic pain." Recently, the vertebral endplates have been identified as another possible pain trigger of the anterior column. This "endplate-driven" model, defined "vertebrogenic pain," is often interconnected with disc degeneration. Diagnosis of vertebrogenic and discogenic pain relies on imaging techniques that isolate pain generators and exclude comorbid conditions. Traditional methods, like radiographs and discography, are augmented by more sensitive methods, including SPECT, CT, and MRI. Morphologic MRI is pivotal in revealing indicators of vertebrogenic (eg, Modic endplate changes) and discogenic pain (eg, disc degeneration and annular fissures). More advanced methods, like ultra-short-echo time imaging, and quantitative MRI further amplify MRI's accuracy in the detection of painful endplate and disc pathology. This review explores the pathophysiology of vertebrogenic and discogenic pain as well as the impact of different imaging modalities in the diagnosis of low back pain. We hope this information can help identify patients who may benefit from personalized clinical treatment and image-guided therapies.

Understanding the etiopathogenesis of lumbar intervertebral disc herniation: From clinical evidence to basic scientific research

Lumbar intervertebral disc herniation, as a leading cause of low back pain, productivity loss, and disability, is a common musculoskeletal disorder that results in significant socioeconomic burdens. Despite extensive clinical and basic scientific research efforts, herniation etiopathogenesis, particularly its initiation and progression, is not well understood. Understanding herniation etiopathogenesis is essential for developing effective preventive measures and therapeutic interventions. Thus, this review seeks to provide a thorough overview of the advances in herniation-oriented research, with a discussion on ongoing challenges and potential future directions for clinical, translational, and basic scientific investigations to facilitate innovative interdisciplinary research aimed at understanding herniation etiopathogenesis. Specifically, risk factors for herniation are identified and summarized, including familial predisposition, obesity, diabetes mellitus, smoking tobacco, selected cardiovascular diseases, disc degeneration, and occupational risks. Basic scientific experimental and computational research that aims to understand the link between excessive mechanical load, catabolic tissue remodeling due to inflammation or insufficient nutrient supply, and herniation, are also reviewed. Potential future directions to address the current challenges in herniation-oriented research are explored by combining known progressive development in existing research techniques with ongoing technological advances. More research on the relationship between occupational risk factors and herniation, as well as the relationship between degeneration and herniation, is needed to develop preventive measures for working-age individuals. Notably, researchers should explore using or modifying existing degeneration animal models to study herniation etiopathogenesis, as such models may allow for a better understanding of how to prevent mild-to-moderately degenerated discs from herniating.

Machine learning algorithm predicts fibrosis-related blood diagnosis markers of intervertebral disc degeneration

BACKGROUND

Intervertebral disc cell fibrosis has been established as a contributing factor to intervertebral disc degeneration (IDD). This study aimed to identify fibrosis-related diagnostic genes for patients with IDD.

METHODS

RNA-sequencing data was downloaded from Gene Expression Omnibus (GEO) database. The diagnostic genes was identified using Random forest based on the differentially expressed fibrosis-related genes (DE-FIGs) between IDD and control samples. The immune infiltration states in IDD and the regulatory network as well as potential drugs targeted diagnostic genes were investigated. Quantitative Real-Time PCR was conducted for gene expression valifation.

RESULTS

CEP120 and SPDL1 merged as diagnostic genes. Substantial variations were observed in the proportions of natural killer cells, neutrophils, and myeloid-derived suppressor cells between IDD and control samples. Further experiments indicated that AC144548.1 could regulate the expressions of SPDL1 and CEP120 by combininghsa-miR-5195-3p and hsa-miR-455-3p, respectively. Additionally, transcription factors FOXM1, PPARG, and ATF3 were identified as regulators of SPDL1 and CEP120 transcription. Notably, 56 drugs were predicted to target these genes. The down-regulation of SPDL1 and CEP120 was also validated.

CONCLUSION

This study identified two diagnostic genes associated with fibrosis in patients with IDD. Additionally, we elucidated their potential regulatory networks and identified target drugs, which offer a theoretical basis and reference for further study into fibrosis-related genes involved in IDD.

Modeling of glycosaminoglycan biosynthesis in intervertebral disc cells

Loss of proteoglycan (PG) is a potential factor responsible for degeneration of the intervertebral disc (IVD). PG consists of a core protein with covalently attached glycosaminoglycan (GAG) chains. The objective of this study was to develop a mathematical model of GAG biosynthesis to investigate the effects of glycolytic enzymes on GAG biosynthesis of IVD cells. A new mathematical model of GAG biosynthesis was developed for IVD cells by incorporating biosynthesis of uridine diphosphate-sugars into the glycolytic pathway. This new model showed good agreement between the model predictions of intracellular ATP content and GAG biosynthesis and experimental data measured at different external glucose levels. The quantitative analyses demonstrated that GAG biosynthesis may be sensitive to the activities of hexokinase (HK) and phosphofructokinase (PFK), especially at low glucose supply, with GAG biosynthesis being significantly enhanced by a slight increase in activities of HK and PFK. This suggests that metabolic reprogramming could be a potential strategy for promoting PG biosynthesis in IVD cells. Furthermore, it was shown that GAG biosynthesis may be promoted by increasing intracellular glutamine concentration or activity of glutamine:fructose-6-phosphate amidotransferase in the hexamine pathway. This study provides a better understanding of the relationship between glycolysis and PG biosynthesis in IVD cells. The theoretical framework developed in this study is useful for studying the role of glycolysis in disc degeneration and developing new preventive and treatment strategies for degeneration of the IVD.

Effects of glucose concentration and oxygen partial pressure on the respiratory metabolism of sheep temporomandibular joint disc cells

Temporomandibular joint (TMJ) disc degeneration is a common disease characterized by a decrease in metabolic function. The present study aimed to investigate the pathogenesis of TMJ disc degeneration by analyzing the effects of oxygen and glucose concentrations on metabolism in a simulated TMJ disc cell growth environment. Cell samples were divided into 10 groups and cultured in different nutritional environments, including 21 and 2% O₂ partial pressures and various glucose concentrations (0, 0.5, 3, 5.5 and 22.5 mmol/l). Cell proliferation, extracellular matrix content, mitochondrial function, and cell metabolism were subsequently analyzed. The results demonstrated that hypoxia and a low glucose concentration inhibited cell growth, and low glucose concentration inhibited extracellular matrix synthesis and adenosine 5'-monophosphate-activated protein kinase expression. Hypoxic conditions also induced a compensatory increase in the number of mitochondria, whereas mitochondrial deformation and swelling were observed in the absence of glucose. According to this study, the primary metabolic pathway of TMJ disc cells is glycolysis. It was concluded that hypoxic conditions and normal glucose concentrations are needed for the growth of TMJ disc cells. Glucose is necessary to ensure cell survival, extracellular matrix synthesis and mitochondrial function. Glucose deficiency may be related to disc degeneration, aging and disease mechanisms.

Intervertebral disc degeneration-Current therapeutic options and challenges

Degeneration of the intervertebral disc (IVD) is a normal part of aging. Due to the spine's declining function and the development of pain, it may affect one's physical health, mental health, and socioeconomic status. Most of the intervertebral disc degeneration (IVDD) therapies today focus on the symptoms of low back pain rather than the underlying etiology or mechanical function of the disc. The deteriorated disc is typically not restored by conservative or surgical therapies that largely focus on correcting symptoms and structural abnormalities. To enhance the clinical outcome and the quality of life of a patient, several therapeutic modalities have been created. In this review, we discuss genetic and environmental causes of IVDD and describe promising modern endogenous and exogenous therapeutic approaches including their applicability and relevance to the degeneration process.

ISSLS PRIZE in basic science 2023: Lactate in lumbar discs-metabolic waste or energy biofuel? Insights from in vivo MRS and T2r analysis following exercise and nimodipine in healthy volunteers

PURPOSE

To quantitatively assess the dynamic changes of Lactate in lumbar discs under different physiological conditions using MRS and T2r.

METHODS

In step1, MRS and T2r sequences were standardized in 10 volunteers. Step2, analysed effects of high cellular demand. 66 discs of 20 volunteers with no back pain were evaluated pre-exercise (EX-0), immediately after targeted short-time low back exercises (EX-1) and 60 min after (EX-2). In Step 3, to study effects of high glucose and oxygen concentration, 50 lumbar discs in 10 volunteers were analysed before (D0) and after 10 days intake of the calcium channel blocker, nimodipine (D1).

RESULTS

Lactate showed a distinctly different response to exercise in that Grade 1 discs with a significant decrease in EX-1 and a trend for normalization in Ex-2. In contrast, Pfirrmann grade 2 and 3 and discs above 40 years showed a higher lactate relative to proteoglycan in EX-0, an increase in lactate EX-1 and mild dip in Ex-2. Similarly, following nimodipine, grade 1 discs showed an increase in lactate which was absent in grade 2 and 3 discs. In contrast, exercise and Nimodipine had no significant change in T2r values and MRS spectrum of proteoglycan, N-acetyl aspartate, carbohydrate, choline, creatine, and glutathione across age groups and Pfirrmann grades.

CONCLUSION

MRS documented changes in lactate response to cellular demand which suggested a 'Lactate Symbiotic metabolic Pathway'. The differences in lactate response preceded changes in Proteoglycan/hydration and thus could be a dynamic radiological biomarker of early degeneration.

GLUT1 is redundant in hypoxic and glycolytic nucleus pulposus cells of the intervertebral disc

Glycolysis is central to homeostasis of nucleus pulposus (NP) cells in the avascular intervertebral disc. Since the glucose transporter, GLUT1, is a highly enriched phenotypic marker of NP cells, we hypothesized that it is vital for the development and postnatal maintenance of the disc. Surprisingly, primary NP cells treated with 2 well-characterized GLUT1 inhibitors maintained normal rates of glycolysis and ATP production, indicating intrinsic compensatory mechanisms. We showed in vitro that NP cells mitigated GLUT1 loss by rewiring glucose import through GLUT3. Of note, we demonstrated that substrates, such as glutamine and palmitate, did not compensate for glucose restriction resulting from dual inhibition of GLUT1/3, and inhibition compromised long-term cell viability. To investigate the redundancy of GLUT1 function in NP, we generated 2 NP-specific knockout mice: Krt19CreERT Glut1fl/fl and Foxa2Cre Glut1fl/fl. There were no apparent defects in postnatal disc health or development and maturation in mutant mice. Microarray analysis verified that GLUT1 loss did not cause transcriptomic alterations in the NP, supporting that cells are refractory to GLUT1 loss. These observations provide the first evidence to our knowledge of functional redundancy in GLUT transporters in the physiologically hypoxic intervertebral disc and underscore the importance of glucose as the indispensable substrate for NP cells.

Co-regulation of Sox9 and TGFβ1 transcription factors in mesenchymal stem cells regenerated the intervertebral disc degeneration

BACKGROUND

Intervertebral disc (IVD) shows aging and degenerative changes earlier than any other body connective tissue. Its repair and regeneration provide a considerable challenge in regenerative medicine due to its high degree of infrastructure and mechanical complexity. Mesenchymal stem cells, due to their tissue resurfacing potential, represent many explanatory pathways to regenerate a tissue breakdown.

METHODS

This study was undertaken to evaluate the co-regulation of Sox9 and TGFβ1 in differentiating human umbilical cord mesenchymal stem cells (hUC-MSC) into chondrocytes. The combinatorial impact of Sox9 and TGFβ1 on hUC-MSCs was examined in vitro by gene expression and immunocytochemical staining. In in vivo, an animal model of IVD degeneration was established under a fluoroscopic guided system through needle puncture of the caudal disc. Normal and transfected MSCs were transplanted. Oxidative stress, pain, and inflammatory markers were evaluated by qPCR. Disc height index (DHI), water content, and gag content were analyzed. Histological examinations were performed to evaluate the degree of regeneration.

RESULTS

hUC-MSC transfected with Sox9+TGFβ1 showed a noticeable morphological appearance of a chondrocyte, and highly expressed chondrogenic markers (aggrecan, Sox9, TGFβ1, TGFβ2, and type II collagens) after transfection. Histological observation demonstrated that cartilage regeneration, extracellular matrix synthesis, and collagen remodeling were significant upon staining with H&E, Alcian blue, and Masson's trichrome stain on day 14. Additionally, oxidative stress, pain, and inflammatory markers were positively downregulated in the animals transplanted with Sox9 and TGFβ1 transfected MSCs.

CONCLUSION

These findings indicate that the combinatorial effect of Sox9 and TGFβ1 substantially accelerates the chondrogenesis in hUC-MSCs. Cartilage regeneration and matrix synthesis were significantly enhanced. Therefore, a synergistic effect of Sox9 and TGFβ1 could be an immense therapeutic combination in the tissue engineering of cartilaginous joint bio-prostheses and a novel candidate for cartilage stabilization.

Dynamic loading leads to increased metabolic activity and spatial redistribution of viable cell density in nucleus pulposus tissue

Background

Nucleus pulposus (NP) cell density is orchestrated by an interplay between nutrient supply and metabolite accumulation. Physiological loading is essential for tissue homeostasis. However, dynamic loading is also believed to increase metabolic activity and could thereby interfere with cell density regulation and regenerative strategies. The aim of this study was to determine whether dynamic loading could reduce the NP cell density by interacting with its energy metabolism.

Methods

Bovine NP explants were cultured in a novel NP bioreactor with and without dynamic loading in milieus mimicking the pathophysiological or physiological NP environment. The extracellular content was evaluated biochemically and by Alcian Blue staining. Metabolic activity was determined by measuring glucose and lactate in tissue and medium supernatants. A lactate-dehydrogenase staining was performed to determine the viable cell density (VCD) in the peripheral and core regions of the NP.

Results

The histological appearance and tissue composition of NP explants did not change in any of the groups. Glucose levels in the tissue reached critical values for cell survival (≤0.5 mM) in all groups. Lactate released into the medium was increased in the dynamically loaded compared to the unloaded groups. While the VCD was unchanged on Day 2 in all regions, it was significantly reduced in the dynamically loaded groups on Day 7 (p ≤ 0.01) in the NP core, which led to a gradient formation of VCD in the group with degenerated NP milieu and dynamic loading (p ≤ 0.05).

Conclusion

It was demonstrated that dynamic loading in a nutrient deprived environment similar to that during IVD degeneration can increase cell metabolism to the extent that it was associated with changes in cell viability leading to a new equilibrium in the NP core. This should be considered for cell injections and therapies that lead to cell proliferation for treatment of IVD degeneration.

Nutrient metabolism of the nucleus pulposus: A literature review

Cells take in, consume, and synthesize nutrients for numerous physiological functions. This includes not only energy production but also macromolecule biosynthesis, which will further influence cellular signaling, redox homeostasis, and cell fate commitment. Therefore, alteration in cellular nutrient metabolism is associated with pathological conditions. Intervertebral discs, particularly the nucleus pulposus (NP), are avascular and exhibit unique metabolic preferences. Clinical and preclinical studies have indicated a correlation between intervertebral degeneration (IDD) and systemic metabolic diseases such as diabetes, obesity, and dyslipidemia. However, a lack of understanding of the nutrient metabolism of NP cells is masking the underlying mechanism. Indeed, although previous studies indicated that glucose metabolism is essential for NP cells, the downstream metabolic pathways remain unknown, and the potential role of other nutrients, like amino acids and lipids, is understudied. In this literature review, we summarize the current understanding of nutrient metabolism in NP cells and discuss other potential metabolic pathways by referring to a human NP transcriptomic dataset deposited to the Gene Expression Omnibus, which can provide us hints for future studies of nutrient metabolism in NP cells and novel therapies for IDD.

Glis1 and oxaloacetate in nucleus pulposus stromal cell somatic reprogramming and survival

Regenerative medicine aims to repair degenerate tissue through cell refurbishment with minimally invasive procedures. Adipose tissue (FAT)-derived stem or stromal cells are a convenient autologous choice for many regenerative cell therapy approaches. The intervertebral disc (IVD) is a suitable target. Comprised of an inner nucleus pulposus (NP) and an outer annulus fibrosus (AF), the degeneration of the IVD through trauma or aging presents a substantial socio-economic burden worldwide. The avascular nature of the mature NP forces cells to reside in a unique environment with increased lactate levels, conditions that pose a challenge to cell-based therapies. We assessed adipose and IVD tissue-derived stromal cells through in vitro transcriptome analysis in 2D and 3D culture and suggested that the transcription factor Glis1 and metabolite oxaloacetic acid (OAA) could provide NP cells with survival tools for the harsh niche conditions in the IVD.

Temperature induces metabolic reprogramming in fish during bacterial infection

Water temperature elevation as a consequence of global warming results in increased incidence of bacterial disease, such as edwardsiellosis, in fish farming. Edwardsiellosis is caused by the bacterial pathogen Edwardsiella tarda and affects many farmed fish including flounder (Paralichthys olivaceus). Currently, the effect of temperature on the metabolic response of flounder to E. tarda infection is unclear. In this study, we found that compared to low temperature (15°C), high temperature (23°C) enhanced E. tarda dissemination in flounder tissues. To examine the impact of temperature on the metabolism of flounder induced by E. tarda, comparative metabolomics were performed, which identified a large number of metabolites responsive to E. tarda invasion and temperature alteration. During E. tarda infection, the metabolic profile induced by elevated temperature was mainly featured by extensively decreased amino acids and TCA intermediates such as succinate, a proven immune regulator. Further, 38 potential metabolite markers of temperature effect (MMTE) in association with bacterial infection were identified. When used as exogenous supplements, two of the MMTE, i.e., L-methionine and UDP-glucose, effectively upregulated the expression of pro-inflammatory cytokines and suppressed E. tarda infection in flounder leukocytes. Taken together, the results of this study indicate an important influence of temperature on the metabolism of flounder during bacterial infection, which eventually affects the survivability of the fish.

Dynamic elastic modulus assessment of the early degeneration model of an intervertebral disc in cynomolgus monkeys with one strike loading

OBJECTIVE

Disc degeneration has long been associated with excessive mechanical loading or acute disc injury. Our goal is to perform a shock load on the functional units of the cynomolgus monkey intervertebral disc and analyze the degree of degeneration of the intervertebral disc through image analysis and comprehensive analysis. The organ model establishes a standard organ culture model and a non-invasive biomechanical evaluation protocol close to the early degeneration of the human intervertebral disc.

METHODS

After modeling, the cynomolgus monkey intervertebral discs were collected and loaded into the dynamic mechanical culture system. The physiological group was loaded with 10% high compressive deformation load for one second, the injury group was punctured with annulus fibrosus, the model group was loaded with 20-50% high compressive deformation, and the nutritional components were a high-glucose group and low-glucose group. After day 3 (short term) and day 10 (long term), samples were collected to analyze cell viability, histomorphology, image analysis for imaging and biomechanical changes.

RESULTS

Both the injury group and the 30-50% strain model group showed signs of early degeneration, including decreased instantaneous compressive stiffness, percent change in gray value, decreased cell viability, AF fissure, and percent increase in dynamic elastic modulus. The glucose-restricted group also showed signs of early disc degeneration in long-term cultures.

CONCLUSION

This study shows that a single shock load can induce early degeneration of healthy cynomolgus monkey intervertebral discs, and 30% strain may be the nociceptive threshold for early degeneration of healthy intervertebral discs. More importantly, a non-invasive biomechanical evaluation scheme of Percentage change in dynamic modulus of elasticity is established, which solves the key scientific problem of how to non-invasively, quantitatively and sensitively detect the development process of early intervertebral disc degeneration and its degree of degeneration in an in vitro organ model.

Two- and three-dimensional in vitro nucleus pulposus cultures: An in silico analysis of local nutrient microenvironments

Background

It is well established that the unique biochemical microenvironment of the intervertebral disc plays a predominant role in cell viability and biosynthesis. However, unless the effect of microenvironmental conditions is primary to a study objective, in vitro culture parameters that are critical for reproducibility are both varied and not routinely reported.

Aims

This work aims to investigate the local microenvironments of commonly used culture configurations, highlighting physiological relevance, potential discrepancies, and elucidating possible heterogeneity across the research field.

Materials and Methods

This work uses nutrient-transport in silico models to reflect on the effect of often underappreciated parameters, such as culture geometry and diffusional distance (vessel, media volume, construct size), seeding density, and external boundary conditions on the local microenvironment of two-dimensional (2D) and three-dimensional (3D) in vitro culture systems.

Results

We elucidate important discrepancies between the external boundary conditions such as the incubator level or media concentrations and the actual local cellular concentrations. Oxygen concentration and cell seeding density were found to be highly influential parameters and require utmost consideration when utilizing 3D culture systems.

Discussion

This work highlights that large variations in the local nutrient microenvironment can easily be established without consideration of several key parameters. Without careful deliberation of the microenvironment within each specific and unique system, there is the potential to confound in vitro results leading to heterogeneous results across the research field in terms of biosynthesis and matrix composition.

Conclusion

Overall, this calls for a greater appreciation of key parameters when designing in vitro experiments. Better harmony and standardization of physiologically relevant local microenvironments are needed to push toward reproducibility and successful translation of findings across the research field.

Immuno-Modulatory Effects of Intervertebral Disc Cells

Low back pain is a highly prevalent, chronic, and costly medical condition predominantly triggered by intervertebral disc degeneration (IDD). IDD is often caused by structural and biochemical changes in intervertebral discs (IVD) that prompt a pathologic shift from an anabolic to catabolic state, affecting extracellular matrix (ECM) production, enzyme generation, cytokine and chemokine production, neurotrophic and angiogenic factor production. The IVD is an immune-privileged organ. However, during degeneration immune cells and inflammatory factors can infiltrate through defects in the cartilage endplate and annulus fibrosus fissures, further accelerating the catabolic environment. Remarkably, though, catabolic ECM disruption also occurs in the absence of immune cell infiltration, largely due to native disc cell production of catabolic enzymes and cytokines. An unbalanced metabolism could be induced by many different factors, including a harsh microenvironment, biomechanical cues, genetics, and infection. The complex, multifactorial nature of IDD brings the challenge of identifying key factors which initiate the degenerative cascade, eventually leading to back pain. These factors are often investigated through methods including animal models, 3D cell culture, bioreactors, and computational models. However, the crosstalk between the IVD, immune system, and shifted metabolism is frequently misconstrued, often with the assumption that the presence of cytokines and chemokines is synonymous to inflammation or an immune response, which is not true for the intact disc. Therefore, this review will tackle immunomodulatory and IVD cell roles in IDD, clarifying the differences between cellular involvements and implications for therapeutic development and assessing models used to explore inflammatory or catabolic IVD environments.

In vivo fluid transport in human intervertebral discs varies by spinal level and disc region

Background

The lumbar discs are large, dense tissues that are primarily avascular, and cells residing in the central region of the disc are up to 6-8 mm from the nearest blood vessel in adults. To maintain homeostasis, disc cells rely on nutrient transport between the discs and adjacent vertebrae. Thus, diminished transport has been proposed as a factor in age-related disc degeneration.

Methods

In this study, we used magnetic resonance imaging (MRI) to quantify diurnal changes in T2 relaxation time, an MRI biomarker related to disc hydration, to generate 3D models of disc fluid distribution and determine how diurnal changes in fluid varied by spinal level. We recruited 10 participants (five males/five females; age: 21-30 years; BMI: 19.1-29.0 kg/m2) and evaluated the T2 relaxation time of each disc at 8:00 AM and 7:00 PM, as well as degeneration grade (Pfirrmann). We also measured disc height, volume, and perimeter in a subset of individuals as a preliminary comparison of geometry and transport properties.

Results

We found that the baseline (AM) T2 relaxation time and the diurnal change in T2 relaxation time were greatest in the cranial lumbar discs, decreasing along the lumbar spine from cranial to caudal. In cranial discs, T2 relaxation times decreased in each disc region (nucleus pulposus [NP], inner annulus fibrosus [IAF], and outer annulus fibrosus [OAF]), whereas in caudal discs, T2 relaxation times decreased in the NP but increased in the AF.

Conclusions

Fluid transport varied by spinal level, where transport was greatest in the most cranial lumbar discs and decreased from cranial to caudal along the lumbar spine. Future work should evaluate what level-dependent factors affect transport.

ISSLS Prize in Bioengineering Science 2022: low rate cyclic loading as a therapeutic strategy for intervertebral disc regeneration

BACKGROUND

The intervertebral disc degenerates with age and has a poor propensity for regeneration. Small molecule transport plays a key role in long-term degradation and repair. Convection (bulk flow), induced by low rate cyclic loading of the intervertebral disc, has been shown to increase transport of small molecules. However, the potential therapeutic benefit of low rate cyclic loading on degenerated discs has not been described. The purpose of this study was to determine if a sustained (daily) low rate cyclic loading regimen could slow, arrest, or reverse intervertebral disc degeneration in the rabbit lumbar spine.

METHODS

Fifty-six New Zealand white rabbits (>12 months old) were designated as either Control (no disc puncture), 8D (disc puncture followed by 8 weeks of degeneration), 16D (disc puncture followed by 16 weeks of degeneration), or Therapy (disc puncture followed by 8 weeks of degeneration and then 8 weeks of daily low rate cyclic loading). Specimens were evaluated by T2 mapping, Pfirrmann scale grading, nucleus volume, disc height index, disc morphology and structure, and proteoglycan content.

RESULTS

In every metric, mean values for the Therapy group fell between Controls and 8D animals. These results suggest that sustained low rate cyclic loading had a therapeutic effect on the already degenerated disc and the regimen promoted signs of regeneration. If these results translate clinically, this approach could fulfil a significant clinical need by providing a means of non-invasively treating intervertebral disc degeneration.

Can Manganese Dioxide Microspheres be Used as Intermediaries to Alleviate Intervertebral Disc Degeneration With Strengthening Drugs?

Degenerative disc disease (DDD) is a pathological condition associated with intervertebral discs (IVDs) that causes chronic back pain. IVD degeneration has become a significant issue in contemporary society. To date, numerous biological therapies have been applied to alleviate the progression of DDD, among which therapeutic protein injection is the most direct and convenient. However, there are some limitations to applying direct protein injection therapy, the most significant being that the efficacy of this method has a short duration, which is a major factor in its effectiveness and the resulting patient satisfaction. How do we solve this problem? Or how can the effectiveness of the treatment be enhanced? It has been proved that manganese dioxide (MnO₂) microspheres, widely used in environmental science, not only regulate the expression of cell genes and cytokines in the microenvironment, but also have the ability to release drugs slowly. We propose that direct injection of protein encapsulated in hollow MnO₂ (h-MnO₂) microspheres could solve the problem of rapid drug release. In addition, the use of a MnO₂ and protein injection in the treatment of DDD may have a synergistic effect, which would be highly significant for the degradation of pro-inflammatory factors in the DDD microenvironment. Therefore, the combination of MnO₂ and protein may provide a new therapeutic approach to alleviate the progression of DDD.

Edifying the Focal Factors Influencing Mesenchymal Stem Cells by the Microenvironment of Intervertebral Disc Degeneration in Low Back Pain

Intervertebral disc degeneration (IVDD) is one of the main triggers of low back pain, which is most often associated with patient morbidity and high medical costs. IVDD triggers a wide range of pathologies and clinical syndromes like paresthesia, weakness of extremities, and intermittent/chronic back pain. Mesenchymal stem cells (MSCs) have demonstrated to possess immunomodulatory functions as well as the capability of differentiating into chondrocytes under appropriate microenvironment conditions, which makes them potentially epitome for intervertebral disc (IVD) regeneration. The IVD microenvironment is composed by niche of cells, and their chemical and physical milieus have been exhibited to have robust influence on MSC behavior as well as differentiation. Nevertheless, the contribution of MSCs to the IVD milieu conditions in healthy as well as degeneration situations is still a matter of debate. It is still not clear which factors, if any, are essential for effective and efficient MSC survival, proliferation, and differentiation. IVD microenvironment clues such as nucleopulpocytes, potential of hydrogen (pH), osmotic changes, glucose, hypoxia, apoptosis, pyroptosis, and hydrogels are capable of influencing the MSCs aimed for the treatment of IVDD. Therefore, clinical usage of MSCs ought to take into consideration these microenvironment clues during treatment. Alteration in these factors could function as prognostic indicators during the treatment of patients with IVDD using MSCs. Thus, standardized valves for these microenvironment clues are warranted.

Reparative effects of chronic intermittent hypobaric hypoxia pre‑treatment on intervertebral disc degeneration in rats

Previous studies have indicated that chronic intermittent hypobaric hypoxia (CIHH) preconditioning can inhibit TNF-α and other related inflammatory cytokines and exerts protective effect on intervertebral disc degeneration disease (IDD) in rats; however, the mechanism is still unclear. The present study aimed to explore the repair mechanisms of CIHH on IDD in rats. In the experiment, 48 adult Sprague-Dawley rats were selected and randomly divided into an experimental group (CIHH-IDD), a degenerative group (IDD) and a control group (CON). The CIHH-IDD group of rats (n=16) were treated with CIHH (simulated 3000 m altitude, 5 h per day, 28 days; P_O2=108.8 mmHg) before disc degeneration surgery. The IDD group of rats (n=16) underwent tail-vertebral intervertebral disc surgery to establish a model of intervertebral disc degeneration. The CON group of rats (n=16) did not receive any treatments. After surgery, the disc height index was calculated using X-ray analysis of rat tail vertebrae, the degeneration process was observed and repair was evaluated by chemically staining degenerative intervertebral disc tissue slices. The expression levels of basic fibroblast growth factor (bFGF), TGFβ1, Collagen I and Collagen II were measured in the intervertebral disc tissue using western blotting; while the expression levels of bFGF, TGFβ1 and hypoxia-inducible factor 1-α (HIF-1α) were measured in rat serum using ELISA. The results demonstrated that: i) The degree of intervertebral disc height degeneration in CIHH-IDD rats was significantly lower compared with that in IDD rats (P<0.05); ii) the expression levels of bFGF, TGFβ1 and HIF-1α were higher in CIHH-IDD rat serum compared with those in IDD rat serum (P<0.05); iii) optical microscopy revealed that the degree of disc degeneration was relatively mild in CIHH-IDD rats; and iv) the protein expression levels of bFGF, TGFβ1 and collagen II were increased in CIHH-IDD rat intervertebral disc tissues compared with those of IDD rats, while the overexpression of collagen I protein was inhibited. Overall, after CIHH pre-treatment, the expression levels of bFGF and TGFβ1 were up-regulated, which play notable roles in repairing degenerative intervertebral discs in rats.

Consolidating and re-evaluating the human disc nutrient microenvironment

Background

Despite exciting advances in regenerative medicine, cell-based strategies for treating degenerative disc disease remain in their infancy. To maximize the potential for successful clinical translation, a more thorough understanding of the in vivo microenvironment is needed to better determine and predict how cell therapies will respond when administered in vivo.

Aims

This work aims to reflect on the in vivo nutrient microenvironment of the degenerating IVD through consolidating what has already been measured together with investigative in silico models.

Materials and Methods

This work uses in silico modeling, underpinned by more recent experimentally determined parameters of degeneration and nutrient transport from the literature, to re-evaluate the current knowledge in terms of grade-specific stages of degeneration.

Results

Through modeling only the metabolically active cell population, this work predicts slightly higher glucose concentrations compared to previous in silico models, while the predicted results show good agreement with previous intradiscal pH and oxygen measurements. Increasing calcification with degeneration limits nutrient transport into the IVD and initiates a build-up of acidity; however, its effect is compensated somewhat by a reduction in diffusional distance due to decreasing disc height.

Discussion

This work advances in silico modeling through a strong foundation of experimentally determined grade-specific input parameters. Taken together, pre-existing measurements and predicted results suggest that metabolite concentrations may not be as critically low as commonly believed, with calcification not appearing to have a detrimental effect at stages of degeneration when cell therapies are an appropriate intervention.

Conclusion

Overall, our initiative is to provoke greater deliberation and consideration of the nutrient microenvironment when performing in vitro cell culture and cell therapy development. This work highlights urgency for robust experimental glucose measurements in healthy and degenerating IVDs, not only to validate in silico models but to significantly advance the field in fully elucidating the nutrient microenvironment and refining in vitro techniques to accelerate clinical translation.

Injectable hydrogels for articular cartilage and nucleus pulposus repair: Status quo and prospects

Osteoarthritis (OA) and chronic low back pain due to degenerative (intervertebral) disc disease (DDD) are two of the major causes of disabilities worldwide, affecting hundreds of millions of people and leading to a high socioeconomic burden. Although OA occurs in synovial joints and DDD occurs in cartilaginous joints, the similarities are striking, with both joints showing commonalities in the nature of the tissues and in the degenerative processes during disease. Consequently, repair strategies for articular cartilage (AC) and nucleus pulposus (NP), the core of the intervertebral disc, in the context of OA and DDD share common aspects. One of such tissue engineering approaches is the use of injectable hydrogels for AC and NP repair. In this review, the state-of-the-art and recent developments in injectable hydrogels for repairing, restoring, and regenerating AC tissue suffering from OA and NP tissue in DDD are summarized focusing on cell-free approaches. The various biomaterial strategies exploited for repair of both tissues are compared, and the synergies that could be gained by translating experiences from one tissue to the other are identified.

Extracellular Vesicles as an Emerging Treatment Option for Intervertebral Disc Degeneration: Therapeutic Potential, Translational Pathways, and Regulatory Considerations

Emergent approaches in regenerative medicine look toward the use of extracellular vesicles (EVs) as a next-generation treatment strategy for intervertebral disc (IVD) degeneration (IVDD) because of their ability to attenuate chronic inflammation, reduce apoptosis, and stimulate proliferation in a number of tissue systems. Yet, there are no Food and Drug Administration (FDA)-approved EV therapeutics in the market with an indication for IVDD, which motivates this article to review the current state of the field and provide an IVD-specific framework to assess its efficacy. In this systematic review, 29 preclinical studies that investigate EVs in relation to the IVD are identified, and additionally, the regulatory approval process is reviewed in an effort to accelerate emerging EV-based therapeutics toward FDA submission and timeline-to-market. The majority of studies focus on nucleus pulposus responses to EV treatment, where the main findings show that stem cell-derived EVs can decelerate the progression of IVDD on the molecular, cellular, and organ level. The findings also highlight the importance of the EV parent cell's pathophysiological and differentiation state, which affects downstream treatment responses and therapeutic outcomes. This systematic review substantiates the use of EVs as a promising cell-free strategy to treat IVDD and enhance endogenous repair.

Exosomes Immunity Strategy: A Novel Approach for Ameliorating Intervertebral Disc Degeneration

Low back pain (LBP), which is one of the most severe medical and social problems globally, has affected nearly 80% of the population worldwide, and intervertebral disc degeneration (IDD) is a common musculoskeletal disorder that happens to be the primary trigger of LBP. The pathology of IDD is based on the impaired homeostasis of catabolism and anabolism in the extracellular matrix (ECM), uncontrolled activation of immunologic cascades, dysfunction, and loss of nucleus pulposus (NP) cells in addition to dynamic cellular and biochemical alterations in the microenvironment of intervertebral disc (IVD). Currently, the main therapeutic approach regarding IDD is surgical intervention, but it could not considerably cure IDD. Exosomes, extracellular vesicles with a diameter of 30–150 nm, are secreted by various kinds of cell types like stem cells, tumor cells, immune cells, and endothelial cells; the lipid bilayer of the exosomes protects them from ribonuclease degradation and helps improve their biological efficiency in recipient cells. Increasing lines of evidence have reported the promising applications of exosomes in immunological diseases, and regarded exosomes as a potential therapeutic source for IDD. This review focuses on clarifying novel therapies based on exosomes derived from different cell sources and the essential roles of exosomes in regulating IDD, especially the immunologic strategy.

Modic Change: An Emerging Complication in the Aging Population

STUDY DESIGN

This was a literature review.

OBJECTIVE

The objective of this study was to review the pathogenesis, prevalence, clinical associations, diagnostic modalities, and treatment options for patients with lower back pain (LBP) associated with Modic change (MC).

SUMMARY OF BACKGROUND DATA

Vertebral body endplates are located between the intervertebral disk and adjacent vertebral body. Despite their crucial roles in nutrition and biomechanical stability, vertebral endplates are extremely susceptible to mechanical failure. Studies examining the events leading to disk degeneration have shown that failure often begins at the endplates. Endplate degeneration with subchondral bone marrow changes were originally noticed on magnetic resonance imaging. These magnetic resonance imaging signal changes were classified as MC.

METHODS

A literature review was conducted on the history, etiology, risk factors, diagnostic modalities, and treatment of LBP with MC.

RESULTS

Type 1 MC refers to the presence of increased vascularization and bone marrow edema within the vertebral body. Type 2 MC involves fatty marrow replacement within the vertebral body. Type 3 MC reflects subchondral bone sclerosis. Despite the original classification, research has supported the notion that MCs possess a transitional nature. Furthermore, type 1 MCs have been strongly associated with inflammation and severe LBP, while types 2 and 3 tend to be more stable and demonstrate less refractory pain. With a strong association to LBP, understanding the etiology of MC is crucial to optimal treatment planning. Various etiologic theories have been proposed including autoimmunity, mechanics, infection, and genetic factors.

CONCLUSIONS

With the aging nature of the population, MC has emerged as an extremely prevalent issue. Research into the pathogenesis of MC is important for planning preventative and therapeutic strategies. Such strategies may include rehabilitation, surgical fixation, stabilization, steroid or cement injection, or antibiotics. Improved diagnostic methods in clinical practice are thus critical to properly identify patients suffering from MC, plan early intervention, and hasten return to functioning.

Role of autophagy in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a leading contributor to low back pain. The intervertebral disc (IVD) is composed of three tissue types: the central gelatinous nucleus pulposus (NP) tissue, the surrounding annulus fibrosus (AF) tissue, and the inferior and superior cartilage endplates. The IVD microenvironment is hypoxic, acidic, hyperosmotic, and low in nutrients because it is mostly avascular. The cellular processes that underlie IDD initiation and progression are still poorly understood. Specifically, a lack of understanding regarding NP cell metabolism and physiology hinders the development of effective therapeutics to treat IDD patients. Autophagy is a vital intracellular degradation process that removes damaged organelles, misfolded proteins, and intracellular pathogens and recycles the degraded components for cellular energy and function. NP cells have adapted to survive within their harsh tissue microenvironment using processes that are largely unknown, and we postulate autophagy is one of these undiscovered mechanisms. In this review, we describe unique features of the IVD tissue, review how physiological stressors impact autophagy in NP cells in vitro, survey the current understanding of autophagy regulation in the IVD, and assess the relationship between autophagy and IDD. Published studies confirm autophagy markers are present in IVD tissue, and IVD cells can regulate autophagy in response to cellular stressors in vitro. However, data are still lacking to determine the exact mechanisms regulating autophagy in IVD cells. More in-depth research is needed to establish whether autophagy is necessary to maintain IVD cell health and validate autophagy as a relevant therapeutic target for treating IDD.

Computational Modeling Intervertebral Disc Pathophysiology: A Review

Lower back pain is a medical condition of epidemic proportion, and the degeneration of the intervertebral disc has been identified as a major contributor. The etiology of intervertebral disc (IVD) degeneration is multifactorial, depending on age, cell-mediated molecular degradation processes and genetics, which is accelerated by traumatic or gradual mechanical factors. The complexity of such intertwined biochemical and mechanical processes leading to degeneration makes it difficult to quantitatively identify cause–effect relationships through experiments. Computational modeling of the IVD is a powerful investigative tool since it offers the opportunity to vary, observe and isolate the effects of a wide range of phenomena involved in the degenerative process of discs. This review aims at discussing the main findings of finite element models of IVD pathophysiology with a special focus on the different factors contributing to physical changes typical of degenerative phenomena. Models presented are subdivided into those addressing role of nutritional supply, progressive biochemical alterations stemming from an imbalance between anabolic and catabolic processes, aging and those considering mechanical factors as the primary source that induces morphological change within the disc. Limitations of the current models, as well as opportunities for future computational modeling work are also discussed.

Patient-specific apparent diffusion maps used to model nutrient availability in degenerated intervertebral discs

INTRODUCTION

In this study, magnetic resonance imaging data was used to (1) model IVD-specific gradients of glucose, oxygen, lactate, and pH; and (2) investigate possible effects of covariate factors (i.e., disc geometry, and mean apparent diffusion coefficient values) on the IVD's microenvironment. Mathematical modeling of the patient's specific IVD microenvironment could be important when selecting patients for stem cell therapy due to the increased nutrient demand created by that treatment.

MATERIALS AND METHODS

Disc geometry and water diffusion coefficients were extracted from MRIs of 37 patients using sagittal T1-weighted images, T2-weighted images, and ADC Maps. A 2-D steady state finite element mathematical model was developed in COMSOL Multiphysics® 5.4 to compute concentration maps of glucose, oxygen, lactate and pH.

RESULTS

Concentration of nutrients (i.e., glucose, and oxygen) dropped with increasing distance from the cartilaginous endplates (CEP), whereas acidity levels increased. Most discs experienced poor nutrient levels along with high acidity values in the inner annulus fibrosus (AF). The disc's physiological microenvironment became more deficient as degeneration progressed. For example, minimum glucose concentration in grade 4 dropped by 31.1% compared to grade 3 (p < 0.0001). The model further suggested a strong effect of the following parameters: disc size, AF and CEP diffusivities, metabolic reactions, and cell density on solute concentrations in the disc (p < 0.05).

CONCLUSION

The significance of this work implies that the individual morphology and physiological conditions of each disc, even among discs of the same Pfirrmann grade, should be evaluated when modeling IVD solute concentrations.

Evidence-Based Network Modelling to Simulate Nucleus Pulposus Multicellular Activity in Different Nutritional and Pro-Inflammatory Environments

Initiation of intervertebral disc degeneration is thought to be biologically driven. This reflects a process, where biochemical and mechanical stimuli affect cell activity (CA) that compromise the tissue strength over time. Experimental research enhanced our understanding about the effect of such stimuli on different CA, such as protein synthesis or mRNA expression. However, it is still unclear how cells respond to their native environment that consists of a "cocktail" of different stimuli that might locally vary. This work presents an interdisciplinary approach of experimental and in silico research to approximate Nucleus Pulposus CA within multifactorial biochemical environments. Thereby, the biochemical key stimuli glucose, pH, and the proinflammatory cytokines TNF-α and IL1β were considered that were experimentally shown to critically affect CA. To this end, a Nucleus Pulposus multicellular system was modelled. It integrated experimental findings from in vitro studies of human or bovine Nucleus Pulposus cells, to relate the individual effects of targeted stimuli to alterations in CA. Unknown stimulus-CA relationships were obtained through own experimental 3D cultures of bovine Nucleus Pulposus cells in alginate beads. Translation of experimental findings into suitable parameters for network modelling approaches was achieved thanks to a new numerical approach to estimate the individual sensitivity of a CA to each stimulus type. Hence, the effect of each stimulus type on a specific CA was assessed and integrated to approximate a multifactorial stimulus environment. Tackled CA were the mRNA expressions of Aggrecan, Collagen types I & II, MMP3, and ADAMTS4. CA was assessed for four different proinflammatory cell states; non-inflamed and inflamed for IL1β, TNF-α or both IL1β&TNF-α. Inflamed cell clusters were eventually predicted in a multicellular 3D agent-based model. Experimental results showed that glucose had no significant impact on proinflammatory cytokine or ADAMTS4 mRNA expression, whereas TNF-α caused a significant catabolic shift in most explored CA. In silico results showed that the presented methodology to estimate the sensitivity of a CA to a stimulus type importantly improved qualitative model predictions. However, more stimuli and/or further experimental knowledge need to be integrated, especially regarding predictions about the possible progression of inflammatory environments under adverse nutritional conditions. Tackling the multicellular level is a new and promising approach to estimate manifold responses of intervertebral disc cells. Such a top-down high-level network modelling approach allows to obtain information about relevant stimulus environments for a specific CA and could be shown to be suitable to tackle complex biological systems, including different proinflammatory cell states. The development of this methodology required a close interaction with experimental research. Thereby, specific experimental needs were derived from systematic in silico approaches and obtained results were directly used to enhance model predictions, which reflects a novelty in this research field. Eventually, the presented methodology provides modelling solutions suitable for multiscale approaches to contribute to a better understanding about dynamics over multiple spatial scales. Future work should focus on an amplification of the stimulus environment by integrating more key relevant stimuli, such as mechanical loading parameters, in order to better approximate native physiological environments.

Effect of environmental and nutritional conditions on the formation of single and mixed-species biofilms and their efficiency in cadmium removal

Remediation of contaminated water and wastewater using biosorption methods has attracted significant attention in recent decades due to its efficiency, convenience and minimised environmental effects. Bacterial biosorbents are normally deployed as a non-living powder or suspension. Little is known about the mechanisms or rates of bacterial attachment to surfaces and effect of various conditions on the biofilm development, as well as efficiency of living biofilms in the removal of heavy metals. In the present study, the effect of environmental and nutritional conditions such as pH, temperature, concentrations of phosphate, glucose, amino acid, nitrate, calcium and magnesium, on planktonic and biofilm growth of single and mixed bacterial cultures, were measured. Actinomyces meyeri, Bacillus cereus, Escherichia coli, Pseudomonas fluorescens strains were evaluated to determine the optimum biofilm growth conditions. The Cd(II) biosorption efficiencies of the mixed-species biofilm developed in the optimum growth condition, were investigated and modelled using Langmuir, Freundlich and Dubnin Radushkevich models. The biofilm quantification techniques revealed that the optimum concentration of phosphate, glucose, amino acid, nitrate, calcium and magnesium for the biofilm development were 25, 10, 1, 1.5, 5 and 0.5 g L^-1, respectively. Further increases in the nutrient concentrations resulted in less biofilm growth. The optimum pH for the biofilm growth was 7 and alkaline or acidic conditions caused significant negative effects on the bacterial attachment and development. The optimum temperatures for the bacterial attachment to the surface were between 25 and 35 °C. The maximum Cd(II) biosorption efficiency (99%) and capacity (18.19 mg g^-1) of the mixed-species biofilm, occurred on day 35 (C_i = 0.1 mg L^-1) and 1 (C_i = 20 mg L^-1) of biofilm growth, respectively. Modelling of the biosorption data revealed that Cd(II) removal by the living biofilm was a physical process by a monolayer of biofilm. The results of present study suggested that environmental and nutritional conditions had a significant effect on bacterial biofilm formation and its efficiency in Cd(II) removal.

Hypoxia Regulates the Extracellular Matrix via Mitogen-Activated Protein Kinases Pathway in Cells Retrieved from the Human Intervertebral Disc

PURPOSE

The present study aimed to identify the physiological characteristics of cells by investigating the change in gene expression and protein levels during extracellular matrix (ECM) synthesis in the intervertebral disc (IVD) under hypoxic conditions.

MATERIALS AND METHODS

To test the effect of oxygen on cell growth and ECM synthesis of chondrocyte-like cells, the cells from IVD were separated and cultured in two hypoxia-mimicking systems: chemical hypoxic conditions using deferoxamine (DFO), and physiological hypoxic conditions using a hypoxic chamber for 7 days. Chondrocyte like cells cultured without DFO and under the normal oxygen concentration (21% O₂ and 5% CO₂, 37°C) served as the controls.

RESULTS

Chondrocyte-like cells cultured in the presence of 6% oxygen demonstrated a 100% increase in cellular proliferation compared to the control. The cells treated with chemical hypoxic conditions demonstrated a dose-dependent increase in the mRNA expression of glucose transporter-1, GAPDH, aggrecan, and type II collagen on Day 1. When treated with 100 µM DFO, the cells showed a 50% increase in the levels of proteoglycan protein on Day 7. The cells treated with chemical hypoxic condition demonstrated increase in sulfated glycosaminoglycan (GAG) protein levels on Day 7. Moreover, the cells cultured in the presence of 6% oxygen showed a 120% increase in sulfated GAG levels on Day 7.

CONCLUSION

The oxygen concentration had an important role in the viability, proliferation, and maturation of chondrocyte-like cells in IVD. In addition, chondrocyte-like cells are sensitive to the concentration of oxygen.

Comprehensive Profile Analysis of Differentially Expressed circRNAs in Glucose Deprivation-Induced Human Nucleus Pulposus Cell Degeneration

Nucleus pulposus (NP) is the core substance to maintain the homeostasis of intervertebral disc and stability of biomechanics. The insufficient supply of nutrition (especially glucose) is an important factor that leads to the degeneration of NP cells. circRNAs play an important role in the process of intervertebral disc degeneration (IDD) by regulating the functions of NP cells. However, glucose deprivation-related circRNAs and their functions in IDD have not been reported. In this study, the differentially expressed circRNAs in NP cells after 0, 6, 12, and 24 h of glucose deprivation culture were detected by a microarray assay. Besides, time series clustering analysis by STEM software obtained the differentially up- and downregulated circRNAs during glucose deficiency. Then, the main functions and pathways of up- and downregulated circRNAs were predicted by the functional enrichment analysis. By constructing the circRNA-miRNA regulatory network, the potential mechanisms of the most differentially expressed circRNAs were predicted. In addition, according to in vitro validation, circ_0075062 was upregulated in degenerating NP tissues and glucose deprivation-induced NP cell degeneration. Based on Sanger sequencing and RNase tolerance assay, circ_0075062 was the circular transcript. Interfering with circ_0075062 expression could potentially alleviate the imbalance of extracellular matrix (ECM) synthesis and degradation in the NP cells induced by glucose deprivation. Together, these findings help us gain a comprehensive understanding of the underlying mechanisms of IDD, and circ_0075062 may be a promising therapeutic target of IDD.

Simulating intervertebral disc cell behaviour within 3D multifactorial environments

MOTIVATION

Low back pain is responsible for more global disability than any other condition. Its incidence is closely related to intervertebral disc (IVD) failure, which is likely caused by an accumulation of microtrauma within the IVD. Crucial factors in microtrauma development are not entirely known yet, probably because their exploration in vivo or in vitro remains tremendously challenging. In silico modelling is, therefore, definitively appealing, and shall include approaches to integrate influences of multiple cell stimuli at the microscale. Accordingly, this study introduces a hybrid Agent-based (AB) model in IVD research and exploits network modelling solutions in systems biology to mimic the cellular behaviour of Nucleus Pulposus cells exposed to a 3D multifactorial biochemical environment, based on mathematical integrations of existing experimental knowledge. Cellular activity reflected by mRNA expression of Aggrecan, Collagen type I, Collagen type II, MMP-3 and ADAMTS were calculated for inflamed and non-inflamed cells. mRNA expression over long periods of time is additionally determined including cell viability estimations. Model predictions were eventually validated with independent experimental data.

RESULTS

As it combines experimental data to simulate cell behaviour exposed to a multifactorial environment, the present methodology was able to reproduce cell death within 3 days under glucose deprivation and a 50% decrease in cell viability after 7 days in an acidic environment. Cellular mRNA expression under non-inflamed conditions simulated a quantifiable catabolic shift under an adverse cell environment, and model predictions of mRNA expression of inflamed cells provide new explanation possibilities for unexpected results achieved in experimental research.

AVAILABILITYAND IMPLEMENTATION

The AB model as well as used mathematical functions were built with open source software. Final functions implemented in the AB model and complete AB model parameters are provided as Supplementary Material. Experimental input and validation data were provided through referenced, published papers. The code corresponding to the model can be shared upon request and shall be reused after proper training.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.