Background. Intervertebral disc degeneration (DD) is a complex age-related condition that constitutes the main risk factor for disabling back pain. DD is assessed using different traits extracted from MR imaging (MRI), normally combined to give summary measures (e.g. Pfirmann score). The aetiology of DD is poorly understood and despite its high heritability (75%), the precise genetic predisposition is yet to be defined. Genome wide association study (GWAS) is used to discover genetic variants associated with a disease or phenotype. It tests variants across the whole genome. It requires large samples to provide adequate but unfortunately there is poor availability of spine imaging data due to the high cost of MRI. We have adopted new methods to examine different MRI traits independently and use the information of those traits to boost GWAS power using specialized statistical software for jointly analyse correlated traits. Methods/Results. We examined DD MRI features disc narrowing, disc bulge, disc signal intensity and osteophyte formation in the TwinsUK cohort who had undergone T2-weighted sagittal spine MRI. GWAS were performed on the four traits. MTAG software was used to boost single trait GWAS power using the information in the other trait GWAS. 9 different loci were identified. Conclusions. Preliminary results suggest genes GDF6, SP1/SP7 are associated with individual trait signal intensity. In addition, novel associated genes with potential for shedding new light on pathogenic mechanisms are identified. Additional cohorts will be included in the design as a replication to test reproducibility of the results. Conflicts of interest: No conflicts of interest. Sources of funding: Funded by Disc4All, EU Horizon 2020, MSCA-2020-ITN-ETN GA: 955735

Biomechanical overloading initiates intervertebral disc degeneration. We hypothesized that this is due to mechanosensitivity of the cells, which break down the extracellular matrix. Previously, we found that overloading in a loaded disc culture system causes upregulation of remodeling- and inflammatory gene expressions. Fourier Transform Infrared Spectroscopy is a novel technique to identify, visualize and quantify ECM. In this research, we first identified novel spectroscopic markers for disc degeneration, and then applied these markers to investigate the first steps into disc degeneration by overloading. In dataset 1, 18 discs of 9 goats were injected with chondroitinase ABC (degenerated) or not (control), and obducted 3 months after injection. This was used to find new spectroscopic markers for degeneration. In dataset 2, 42 goat discs were loaded with a physiological loading regime (50–150N) or overloading (50–400N) in a loaded disc culture system. In 18 of these discs, the cell activity was diminished in advance by freeze-thaw cycles and culturing on saline alone (non-vital group)). 24 additional discs were cultured in culture medium immediately post-mortem (vital group). Thereby, we are able to control whether the effect of the overloading is due to cell activity. The discs were fixed in formaldehyde, and 4 μm mid-sagittal were mounted to steel reflectance slides. Infrared spectroscopic mosaic images (23 × 57 images) were collected in transflectance mode at a spectral region of 1025–1150 cm. −1. Data was pre-processed by second derivative transformation and MCR-MALS with two factors. The two factors were transferable between datasets, confirming the reliability. The first factor represents proteoglycans, as confirmed by Saffrin-O staining. In dataset 1, the degenerated group had less proteoglycan factor overall, especially in the nucleus (p<0.05). The second factor was found to have a lower entropy (p<0.01), showing a disorganization in the matrix. In dataset 2, no significant reduction in proteoglycan was found due to overloading in any group. However, the entropy was lower in the overloaded vital group (p<0.05), but not in the overloaded non-vital group (p>0.5). Therefore, we conclude that infrared spectroscopy is a promising tool to investigate early disc degeneration. Overloading can cause changes in the extracellular matrix, but only due to cell activity. Entropy is an early marker for early disc degeneration, implying that cutting of the extracellular matrix by cell activity is the first step into intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is responsible for severe clinical symptoms including chronic back pain. Galectins are a family of carbohydrate-binding proteins, some of which can induce functional disease markers in IVD cells and other musculoskeletal diseases. Galectins −4 and −8 were shown to trigger disease-promoting activity in chondrocytes but their effects on IVD cells have not been investigated yet. This study elucidates the role of galectin-4 and −8 in IVD degeneration. Immunohistochemical evidence for the presence of galectin-4 and −8 in the IVD was comparatively provided in specimens of 36 patients with spondylochondrosis, spondylolisthesis, or spinal deformity. Confocal microscopy revealed co-localization of galectin-4 and −8 in chondrocyte clusters of degenerated cartilage. The immunohistochemical presence of galectin-4 correlated with histopathological and clinical degeneration scores of patients, whereas galectin-8 did not show significant correlations. The specimens were separated into annulus fibrosus (AF), nucleus pulposus (NP) and endplate, which was confirmed histologically. Separate cell cultures of AF and NP (n=20) were established and characterized using cell type-specific markers. Potential binding sites for galectins including sialylated N-glycans and LacdiNAc structures were determined in AF and NP cells using LC/ESI-MS-MS. To assess galectin functions, cell cultures were treated with recombinant galectin-4 or −8, in comparison to IL-1β, and analyzed using RT-qPCR and In-cell Western blot. In vitro, both galectins triggered the induction of functional disease markers (CXCL8 and MMP3) on mRNA level and activated the nuclear factor-kB pathway. NP cells were significantly more responsive to galectin-8 and Il-1β than AF cells. Phosphorylation of p-65 was time-dependently induced by both galectins in both cell types to a comparable extent. Taken together, this study provides evidence for a functional role of glycobiological processes in IVD degeneration and highlights galectin-4 and −8 as regulators of pro-inflammatory and degrative processes in AF and NP cells

Using deep learning and image processing technology, a standardized automatic quantitative analysis systerm of lumbar disc degeneration based on T2MRI is proposed to help doctors evaluate the prognosis of intervertebral disc (IVD) degeneration. A semantic segmentation network BianqueNet with self-attention mechanism skip connection module and deep feature extraction module is proposed to achieve high-precision segmentation of intervertebral disc related areas. A quantitative method is proposed to calculate the signal intensity difference (SI) in IVD, average disc height (DH), disc height index (DHI), and disc height-to-diameter ratio (DHR). According to the correlation analysis results of the degeneration characteristic parameters of IVDs, 1051 MRI images from four hospitals were collected to establish the quantitative ranges for these IVD parameters in larger population around China. The average dice coefficients of the proposed segmentation network for vertebral bodies and intervertebral discs are 97.04% and 94.76%, respectively. The designed parameters of intervertebral disc degeneration have a significant negative correlation with the Modified Pfirrmann Grade. This procedure is suitable for different MRI centers and different resolution of lumbar spine T2MRI (ICC=.874~.958). Among them, the standard of intervertebral disc signal intensity degeneration has excellent reliability according to the modified Pfirrmann Grade (macroF1=90.63%~92.02%). we developed a fully automated deep learning-based lumbar spine segmentation network, which demonstrated strong versatility and high reliability to assist residents on IVD degeneration grading by means of IVD degeneration quantitation

Low back pain affects 80% of the population with half of cases attributed to intervertebral disc (IVD) degeneration. However, the majority of treatments focus on pain management, with none targeting the underlying pathophysiological causes. PCRX-201 presents a novel gene therapy approach that addresses this issue. PCRX-201 codes for interleukin-1 receptor antagonist (IL-1Ra), the natural inhibitor of the pro-inflammatory cytokine IL-1, which orchestrates the catabolic degeneration of the IVD. Our objective here is to determine the ability of PCRX-201 to infect human nucleus pulposus (NP) cells and tissue to increase the production of IL-1Ra and assess downstream effects on catabolic protein production. Degenerate human NP cells and tissue explants were infected with PCRX-201 at 0 or 3000 multiplicities of infection (MOI) and subsequently cultured for 5 days in monolayer (n=7), 21 days in alginate beads (n=6) and 14 days in tissue explants (n=5). Cell culture supernatant was collected throughout culture duration and downstream targets associated with pain and degeneration were assessed using ELISA. IL-1Ra production was increased in NP cells and tissue infected with PCRX-201. The production of downstream catabolic proteins such as IL-1β, IL-6, MMP3, ADAMTS4 and VEGF was decreased in both 3D-cultured NP cells and tissue explants. Here, we have demonstrated that a novel gene therapy, PCRX-201, is able to infect and increase the production of IL-1Ra in degenerate NP cells and tissue in vitro. The increase of IL-1Ra also resulted in a decrease in the production of a number of pro-inflammatory and catabolic proteins, suggesting PCRX-201 enables the inhibition of IL-1-driven IVD degeneration. At present, no treatments for IVD degeneration target the underlying pathology. The ability of FX201 to elicit anti-catabolic responses is promising and warrants further investigation in vitro and in vivo, to determine the efficacy of this exciting, novel gene therapy

Aims. Rotator cuff (RC) injuries are characterized by tendon rupture, muscle atrophy, retraction, and fatty infiltration, which increase injury severity and jeopardize adequate tendon repair. Epigenetic drugs, such as histone deacetylase inhibitors (HDACis), possess the capacity to redefine the molecular signature of cells, and they may have the potential to inhibit the transformation of the fibro-adipogenic progenitors (FAPs) within the skeletal muscle into adipocyte-like cells, concurrently enhancing the myogenic potential of the satellite cells. Methods. HDACis were added to FAPs and satellite cell cultures isolated from mice. The HDACi vorinostat was additionally administered into a RC injury animal model. Histological analysis was carried out on the isolated supra- and infraspinatus muscles to assess vorinostat anti-muscle degeneration potential. Results. Vorinostat, a HDACi compound, blocked the adipogenic transformation of muscle-associated FAPs in culture, promoting myogenic progression of the satellite cells. Furthermore, it protected muscle from degeneration after acute RC in mice in the earlier muscle degenerative stage after tenotomy. Conclusion. The HDACi vorinostat may be a candidate to prevent early muscular degeneration after RC injury. Cite this article: Bone Joint Res 2024;13(4):169–183

Introduction. Vertebral compression fractures are the most common type of osteoporotic fracture. Though 89% of clinical fractures occur anteriorly, it is challenging to replicate these ex vivo with the underlying intervertebral discs (IVDs) present. Furthermore, the role of disc degeneration in this mechanism is poorly understood. Understanding how disc morphology alters vertebral strain distributions may lead to the utilisation of IVD metrics in fracture prediction, or inform surgical decision-making regarding instrumentation type and placement. Aim. To determine the effect of disc degeneration on the vertebral trabecular bone strain distributions in axial compression and flexion loading. Methods. Eight cadaveric thoracolumbar segments (T11-L3) were prepared (N=4 axial compression, N=4 flexion). µCT-based digital volume correlation was used to quantify trabecular strains. A bespoke loading device fixed specimens at the resultant displacement when loaded to 50N and 800N. Flexion was achieved by adding 6° wedges. Disc degeneration was quantified with Pfirrmann grading and T2 relaxation times. Results. Anterior axial strains were 80.9±39% higher than the posterior region in flexion (p<0.01), the ratio of which was correlated with T2 relaxation time (R. 2. =0.80, p<0.05). In flexion, the central-to-peripheral axial strain ratio in the endplate region was significantly higher when the underlying IVDs were non-degenerated relative to degenerated (+38.1±12%, p<0.05). No significant differences were observed in axial compression. Conclusion. Disc degeneration is a stronger determinant of the trabecular strain distribution when flexion is applied. Load transfer through non-degenerate IVDs under flexion appears to be more centralised, suggesting that disc degeneration predisposes flexion-type compression fractures by shifting high strains anteriorly. Conflicts of interest. The authors declare none. Sources of funding. This work was funded by the Engineering & Physical Sciences Research Council (EP/V029452/1), and Back-to-Back

Aims. A revision for periprosthetic joint infection (PJI) in total hip arthroplasty (THA) has a major effect on the patient’s quality of life, including walking capacity. The objective of this case control study was to investigate the histological and ultrastructural changes to the gluteus medius tendon (GMED) in patients revised due to a PJI, and to compare it with revision THAs without infection performed using the same lateral approach. Methods. A group of eight patients revised due to a PJI with a previous lateral approach was compared with a group of 21 revised THAs without infection, performed using the same approach. The primary variables of the study were the fibril diameter, as seen in transmission electron microscopy (TEM), and the total degeneration score (TDS), as seen under the light microscope. An analysis of bacteriology, classification of infection, and antibiotic treatment was also performed. Results. Biopsy samples from the GMED from infected patients revealed a larger fibril diameter than control patients, as seen in the TEM (p < 0.001). Uninfected patients were slightly older and had their revisions performed significantly later than the infected patients. Histologically, samples from infected patients revealed significantly more vascularity (p < 0.001), the presence of glycosaminoglycans (p < 0.001), and a higher TDS (p = 0.003) than the control patients. The majority of patients had staphylococcal infections of various species. Conclusion. More histological degeneration in the GMED was found in patients undergoing THA revision surgery due to PJI than in patients undergoing THA revision surgery due to other reasons. Cite this article: Bone Jt Open 2023;4(8):628–635

Intervertebral disc (IVD) degeneration is the most frequent cause of Low Back Pain (LBP) affecting nearly 80% of the population [1]. Current treatments fail to restore a functional IVD or to provide a long-term solution, so, there is an urgent need for novel therapeutic strategies. We have defined the IVD extracellular matrix (ECM) profile, showing that the pro-regenerative molecules Collagen type XII and XIV, are uniquely expressed during fetal stages [2]. Now we propose the first fetal injectable biomaterial to regenerate the IVD. Fetal decellularized IVD scaffolds were recellularized with adult IVD cells and further implanted in vivo to evaluate their anti-angiogenic potential. Young decellularized IVD scaffolds were used as controls. Finally, a large scale protocol to produce a stable, biocompatible and easily injectable fetal IVD-based hydrogel was developed. Fetal scaffolds were more effective at promoting Aggrecan and Collagen type II expression by IVD cells. In a Chorioallantoid membrane assay, only fetal matrices showed an anti-angiogenic potential. The same was observed in vivo when the angiogenesis was induced by human NP cells. In this context, human NP cells were more effective in GAG synthesis within a fetal microenvironment. Vaccum-assisted perfusion decellularized IVDs were obtained, with high DNA removal and sGAG retention. Hydrogel pre-solution passed through 21-30G needles. IVD cells seeded on the hydrogels initially decreased metabolic activity, but increased up to 70% at day 7, while LDH assay revealed cytotoxicity always below 30%. This study will open new avenues for the establishment of a disruptive treatment for IVD degeneration with a positive impact on the angiogenesis associated with LBP, and on the improvement of patients’ quality of life. Acknowledgements: Financial support was obtained from EUROSPINE, ON Foundation and FCT (Fundação para a Ciência e a Tecnologia)

A key cause of low back pain is the degeneration of the intervertebral disc (IVD). Causality between infection of the IVD and its degenerative process gained great interest over the last decade. Granville Smith et al. (2021) identified 36 articles from 34 research studies investigating bacteria in human IVDs. Bacteria was identified in 27 studies, whereas 9 attributed bacterial presence to contamination. Cutibacterium acnes was the most abundant, followed by coagulase-negative staphylococcus. However, whether bacteria identified were present in vivo or represent perioperative contamination remains unclear. This study investigated whether bacteria are present in IVDs and what potential effects they may have on native disc cells. Immunohistochemical staining for Gram positive bacteria was performed on human IVD tissue to identify presence and characterise bacterial species. Nucleus pulposus (NP) cells in monolayer and 3D alginate were stimulated with LPS and Peptidoglycan (0.1-50 µg/ml) for 48hrs. Following stimulation qPCR for factors associated with disc degeneration including matrix genes, matrix degrading enzymes, cytokines, neurotrophic factors and angiogenic factors and conditioned media collected for ELISA and luminex analysis. Gram positive bacteria was detected within human IVD tissue. Internalisation of bacteria by NP cells influenced the cell and nuclei morphology. Preliminary results of exposure of NP cells to bacterial components indicate that LPS as well as Peptidoglycan increase IL-8 and ADAMTS-4 gene expression following 48 hours of stimulation with a dose response seen for IL-8 induction by peptidoglycan compared to the control group. Underlining these results, IL-8 protein release was increased for treated groups compared to non-treated control. Further analysis is underway investigating other output measures and additional biological repeats. This study has demonstrated bacteria are present within IVD cells within IVD tissue removed from degenerate IVD and is determining the potential influence of these on disc degeneration

Intervertebral disc (IVD) degeneration is a pathological process often associated with chronic back pain and considered a leading cause of disability worldwide. 1. During degeneration, progressive structural and biochemical changes occur, leading to blood vessel and nerve ingrowth and promoting discogenic pain. 2. In the last decades, several cytokines have been applied to IVD cells in vitro to investigate the degenerative cascade. Particularly, IL-10 and IL-4 have been predicted as important anabolic factors in the IVD according to a regulatory network model based in silico approach. 3. Thus, we aim to investigate the potential presence and anabolic effect of IL-10 and IL-4 in human NP cells (in vitro) and explants (ex vivo) under hypoxia (5% O2) after a catabolic induction. Primary human NP cells were expanded, encapsulated in 1.2% alginate beads (4 × 106 cells/ml) and cultured for two weeks in 3D for phenotype recovery while human NP explants were cultured for five days. Afterwards, both alginate and explant cultures were i) cultured for two days and subsequently treated with 10 ng/ml IL-10 or IL-4 (single treatments) or ii) stimulated with 0.1 ng/ml IL-1β for two days and subsequently treated with 10 ng/ml IL-10 or IL-4 (combined treatments). The presence of IL-4 receptor, IL-4 and IL-10 was confirmed in human intact NP tissue (Fig 1). Additionally, IL-4 single and combined treatments induced a significant increase of proinflammatory protein secretion in vitro (Fig. 2A-C) and ex vivo (Fig. 2D and E). In contrast, no significant differences were observed in the secretome between IL-10 single and combined treatments compared to control group. Overall, IL-4 containing treatments promote human NP cell and explant catabolism in contrast to previously reported IL-4 anti-inflammatory performance. 4. Thus, a possible pleiotropic effect of IL-4 could occur depending on the IVD culture and environmental condition. Acknowledgements: This project was supported by the Marie Skłodowska Curie International Training Network “disc4all” under the grant agreement #955735. For any figures and tables, please contact the authors directly

Degenerative disc disease (DDD) is a common cause of lower back pain. Calcification of the intervertebral disc (IVD) has been correlated with DDD, and is especially prevalent in scoliotic discs. The appearance of calcium deposits has been shown to increase with age, and its occurrence has been associated with several other disorders such as hyperparathyroidism, chondrocalcinosis, and arthritis. Trauma, vertebral fusion and infection have also been shown to increase the incidence of IVD calcification. Our data indicate that Ca. 2+. and expression of the extracellular calcium-sensing receptor (CaSR) are significantly increased in mild to severely degenerative human IVDs. In this study, we evaluated the effects of Ca. 2+. and CaSR on the degeneration and calcification of IVDs. Human donor lumbar spines of Thompson grade 2, 3 and 4 through organ donations within 24 hs after death. IVD cells, NP and AF, were isolated from tissue by sequential digestion with Pronase followed by Collagenase. Cells were expanded for 7 days under standard cell culture conditions. Immunohistochemistry was performed on IVD tissue to validate the grade and expression of CaSR. Free calcium levels were also measured and compared between grades. Immunocytochemistry, Western blotting and RT-qPCR were performed on cultured NP and AF cells to demonstrate expression of CaSR, matrix proteins aggrecan and collagen, catabolic enzymes and calcification markers. IVD cells were cultured in increasing concentrations of Ca. 2+. [1.0-5.0 mM], CaSR allosteric agonist (cincalcet, 1 uM), and IL-1b [5 ng/mL] for 7 days. Ex vivo IVD organ cultures were prepared using PrimeGrowth Disc Isolation System (Wisent Bioproducts, Montreal, Quebec). IVDs were cultured in 1.0, 2.5 mM Ca. 2+. or with cinacalcet for 21 days to determine effects on disc degeneration, calcification and biomechanics. Complex modulus and structural stiffness of disc tissues was determined using the MACH-1 mechanical testing system (Biomomentum, Laval, Quebec). Ca. 2+. dose-dependently decreased matrix protein synthesis of proteoglycan and Col II in NP and AF cells, similar to treatment with IL-1b. (n = 4). Contrarily to IL-1b, Ca. 2+. and cincalcet did not significantly increase the expression of catabolic enzymes save ADAMTS5. Similar effects were observed in whole organ cultures, as Ca. 2+. and cinacalcet decreased proteoglycan and collagen content. Although both Ca. 2+. and cinacalcet increased the expression of alkaline phosphatase (ALP), only in Ca. 2+. -treated IVDs was there evidence of calcium deposits in NP and AF tissues as determined by von Kossa staining. Biomechanical studies on Ca. 2+. and cinacalcet-treated IVDs demonstrated decreases in complex modulus (p<0.01 and p<0.001, respectively; n=5), however, only Ca. 2+. -treated IVDs was there significant increases stiffness in NP and AF tissues (p<0.001 and p<0.05, respectively; n=3). Our results suggest that changes in the local concentrations of calcium and activation of CaSR affects matrix protein synthesis, calcification and IVD biomechanics. Ca. 2+. may be a contributing factor in IVD degeneration and calcification

Aims. This study aimed, through bioinformatics analysis and in vitro experiment validation, to identify the key extracellular proteins of intervertebral disc degeneration (IDD). Methods. The gene expression profile of GSE23130 was downloaded from the Gene Expression Omnibus (GEO) database. Extracellular protein-differentially expressed genes (EP-DEGs) were screened by protein annotation databases, and we used Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) to analyze the functions and pathways of EP-DEGs. STRING and Cytoscape were used to construct protein-protein interaction (PPI) networks and identify hub EP-DEGs. NetworkAnalyst was used to analyze transcription factors (TFs) and microRNAs (miRNAs) that regulate hub EP-DEGs. A search of the Drug Signatures Database (DSigDB) for hub EP-DEGs revealed multiple drug molecules and drug-target interactions. Results. A total of 56 EP-DEGs were identified in the differential expression analysis. EP-DEGs were enriched in the extracellular structure organization, ageing, collagen-activated signalling pathway, PI3K-Akt signalling pathway, and AGE-RAGE signalling pathway. PPI network analysis showed that the top ten hub EP-DEGs are closely related to IDD. Correlation analysis also demonstrated a significant correlation between the ten hub EP-DEGs (p＜0.05), which were selected to construct TF–gene interaction and TF–miRNA coregulatory networks. In addition, ten candidate drugs were screened for the treatment of IDD. Conclusion. The findings clarify the roles of extracellular proteins in IDD and highlight their potential as promising novel therapeutic targets. Cite this article: Bone Joint Res 2023;12(9):522–535

Low back pain is strongly associated with degeneration of the intervertebral disc (IVD). During degeneration, altered matrix synthesis and increased matrix degradation, together with accompanied cell loss is seen particularly in the nucleus pulposus (NP). It has been proposed that notochordal (NC) cells, embryonic precursors for the cells within the NP, could be utilized for mediating IVD regeneration. However, injectable biomaterials are likely to be required to support their phenotype and viability within the degenerate IVD. Therefore, viability and phenotype of NC cells were analysed and compared within biomaterial carriers subjected to physiological oxygen conditions over a four-week period were investigated. Porcine NC cells were incorporated into three injectable hydrogels: NPgel (a L-pNIPAM-co-DMAc hydrogel), NPgel with decellularized NC-matrix powder (dNCM) and Albugel (an albumin/ hyaluronan hydrogel). The NCs and biomaterials constructs were cultured for up to four weeks under 5% oxygen (n=3 biological repeats). Histological, immunohistochemical and glycosaminoglycans (GAG) analysis were performed to investigate NC viability, phenotype and extracellular matrix synthesis and deposition. Histological analysis revealed that NCs survive in the biomaterials after four weeks and maintained cell clustering in NPgel, Albugel and dNCM/NPgel with maintenance of morphology and low caspase 3 staining. NPgel and Albugel maintained NC cell markers (brachyury and cytokeratin 8/18/19) and extracellular matrix (collagen type II and aggrecan). Whilst Brachyury and Cytokeratin were decreased in dNCM/NPgel biomaterials, Aggrecan and Collagen type II was seen in acellular and NC containing dNCM/NPgel materials. NC containing constructs excreted more GAGs over the four weeks than the acellular controls. NC cells maintain their phenotype and characteristic features in vitro when encapsulated into biomaterials. NC cells and biomaterial construct could potentially become a therapy to treat and regenerate the IVD

Purpose of study and background. Degeneration of the intervertebral disc is a strong contributor of low back pain. Studies have shown that both, mechanical unloading and overloading, lead to disc degeneration. This is intuitively clear if one considers that an intervertebral disc essentially is a poro-elastic material embedded with cells, which depend on fluid flow for the transport of nutrients and waste products. As such, mechanical loading is also required for regeneration. It is unclear, however, how much loading is beneficial or detrimental for the healthy or degenerated disc. Methods and Results. We developed a loaded disc culture system for the long-term study of disc physiology. This way we could control both the mechanical and biochemical conditions. If no loading was applied, about half of the cells died within a week. Cells died under a low dynamic loading regime after three weeks. A diurnal loading regime rescued cell viability, gene expression profile and mechanical behavior of the discs. Both static and dynamic overloading induced damage to the discs and led to catabolic and inflammatory gene expressions. Conclusion. Intervertebral discs need a certain dosage of mechanical loading to remain viable. Under overloading, cells deform, change gene expression and become degenerative. The matrix is also remodeled, thereby further decreasing the hydrostatic pressure on the cells and increasing their deformation. This induces a vicious circle of disc degeneration, which needs to be reversed in order to repair the disc. The loaded disc culture system also allows evaluating new therapies for disc degeneration. There are no conflicts of interest. Funded by ZonMW program “Alternatives for live animal testing”, grant #11400090;. BioMedical Materials Program, grant # P2.01 IDiDas; Dutch Arthritis Funds, personal grant KSE

Objectives. Low back pain is strongly associated with degeneration of the intervertebral disc (IVD). During degeneration, altered matrix synthesis and increased matrix degradation, together with accompanied cell loss is seen particularly in the nucleus pulposus (NP). It has been proposed that notochordal (NC) cells, embryonic precursors for the cells within the NP, could be utilized for mediating IVD regeneration. However, injectable biomaterials are likely to be required to support their phenotype and viability within the degenerate IVD. Therefore, viability and phenotype of NC cells were analysed and compared within biomaterial carriers subjected to physiological oxygen conditions over a four-week period were investigated. Methodology. Porcine NC cells were incorporated into three injectable hydrogels: NPgel (a L-pNIPAM-co-DMAc hydrogel), NPgel with decellularized NC-matrix powder (dNCM) and Albugel (an albumin/ hyaluronan hydrogel). The NCs and biomaterials constructs were cultured for up to four weeks under 5% oxygen (n=3 biological repeats). Histological, immunohistochemical and glycosaminoglycans (GAG) analysis were performed to investigate NC viability, phenotype and extracellular matrix synthesis and deposition. Results. Histological analysis revealed that NCs survive in the biomaterials after four weeks and maintained cell clustering in NPgel, Albugel and dNCM/NPgel. NPgel and Albugel maintained NC cell markers and extracellular matrix. NC containing constructs excreted more GAGs over the four weeks than the acellular controls. Conclusion. NC cells maintain their phenotype and characteristic features in vitro when encapsulated into biomaterials. NC cells and biomaterial construct could potentially become a therapy to treat and regenerate the IVD. Conflicts of interest: No conflicts of interest. Sources of funding: This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 825925

Low back pain is thought to relate to intervertebral disc (IVD) degeneration. Although the mechanisms have not been clearly identified, exhaustion of nucleus pulposus cells and their producing matrix is regarded as one cause. The matrix of the IVD is continuously replenished and remodeled by tissue-specialized cells and are crucial in supporting the IVD function. However, due to aging, trauma, and genetic and lifestyle factors, the cells can lose their potency and viability, thereby limiting their collective matrix production capacity. We have discovered the link between loss of angiopoietin-1 receptor (Tie2)-positive human NP progenitor cells (NPPC) and IVD degeneration. Tie2+ cells were characterized as undifferentiated cells with multipotency and possessing high self-renewal abilities. Thus we and others have proposed Tie2+ NPPC as a potent cell source for regenerative cell therapies against IVD degeneration. However, their utilization is hindered by low Tie2-expressing cell yields from NP tissue, in particular from commonly available older and degenerated tissue sources. Moreover, NPPC show a rapid Tie2 decrease due to cell differentiation as part of standard culture processes. As such, a need exists to optimize or develop new culture methods that enable the maintenance of Tie2-expressing NPPC. Trials to overcome these difficulties will be shared

Purpose of study and background. Low back pain affects 80% of the population at some point in their lives with 40% of cases attributed to intervertebral disc (IVD) degeneration. A number of potential regenerative approaches are under investigation worldwide, however their translation to clinic is currently hampered by an appropriate model for testing prior to clinical trials. Therefore, a more representative large animal model for IVD degeneration is needed to mimic human degeneration. Here we investigate a caprine IVD degeneration model in a loaded disc culture system which can mimic the native loading environment of the disc. Methods and Results. Goat discs were excised and cultured in a bioreactor under diurnal, simulated-physiological loading (SPL) conditions, following 3 days pre load, IVDs were degenerated enzymatically for 2hrs and subsequently loaded for 10 days under physiological loading. A PBS injected group was used as controls. Disc deformation was continuously monitored and changes in disc height recovery quantified using stretched-exponential fitting. Histological staining was performed on caprine discs to assess extracellular matrix production and immunohistochemistry performed to determine expression of catabolic protein expression. The injection of collagenase and cABC induced mechanical behavior akin to that seen in human degeneration. A decrease in collagens and glycosaminoglycans (GAGs) was seen in enzyme injected discs, which was accompanied by increased cellular expression for degradative enzymes and catabolic cytokines. Conclusion. This model provides a reproducible model of IVD degeneration which mimics human degeneration. This model allows the testing of biomaterials and other potential treatments of IVD degeneration on a scale more representative of the human disc. There are no conflicts of interest. Funded by MRC and Versus Arthritis

Intervertebral disc degeneration is a common cause of low-back pain, the musculoskeletal disorder with the largest impact world-wide. The complex disease is however not yet well understood, and no treatment is available. This is somewhat in contrast with osteoarthritis, a subject of more extensive research. Intervertebral disc degeneration may though be a type of osteoarthritis, as other vertebrates have a diarthrodial joint instead of an intervertebral disc. We describe the parallel in view of the anatomy, composition and degeneration of the intervertebral disc and articular joint. Not only different embryonic origin and anatomy suggest significant differences between the intervertebral disc and the synovial joint, but their biomechanical properties also partly differ, as articulation is one of the key properties of a synovial joint and does not occur in the intervertebral disc. However, both tissues provide flexibility and are able to endure compressive loads, and both cell behavior and extracellular matrix appear much the same, mainly existing of chondrocytes, proteoglycans and collagen type II, suggesting that the environment of the cell is more important to its behavior than embryonic origin. Moreover, great similarities are found in the inflammatory cytokines, which are mainly IL-1β and TNF-α, and matrix-degrading factors (i.e. MMPs and ADAMTSs) involved in the cascade of degeneration, resulting in overlapping clinical and radiological features such as loss of joint space, subchondral sclerosis, and the formation of osteophytes, causing pain and morning stiffness. Therefore, we state that disc degeneration can result in the osteoarthritic intervertebral disc. This point of view may enhance the synergy between both fields of research, and potentially provide new regenerative strategies for intervertebral disc degeneration

Aims. In this investigation, we administered oxidative stress to nucleus pulposus cells (NPCs), recognized DNA-damage-inducible transcript 4 (DDIT4) as a component in intervertebral disc degeneration (IVDD), and devised a hydrogel capable of conveying small interfering RNA (siRNA) to IVDD. Methods. An in vitro model for oxidative stress-induced injury in NPCs was developed to elucidate the mechanisms underlying the upregulation of DDIT4 expression, activation of the reactive oxygen species (ROS)-thioredoxin-interacting protein (TXNIP)-NLRP3 signalling pathway, and nucleus pulposus pyroptosis. Furthermore, the mechanism of action of small interfering DDIT4 (siDDIT4) on NPCs in vitro was validated. A triplex hydrogel named siDDIT4@G5-P-HA was created by adsorbing siDDIT4 onto fifth-generation polyamidoamine (PAMAM) dendrimer using van der Waals interactions, and then coating it with hyaluronic acid (HA). In addition, we established a rat puncture IVDD model to decipher the hydrogel’s mechanism in IVDD. Results. A correlation between DDIT4 expression levels and disc degeneration was shown with human nucleus pulposus and needle-punctured rat disc specimens. We confirmed that DDIT4 was responsible for activating the ROS-TXNIP-NLRP3 axis during oxidative stress-induced pyroptosis in rat nucleus pulposus in vitro. Mitochondria were damaged during oxidative stress, and DDIT4 contributed to mitochondrial damage and ROS production. In addition, siDDIT4@G5-P-HA hydrogels showed good delivery activity of siDDIT4 to NPCs. In vitro studies illustrated the potential of the siDDIT4@G5-P-HA hydrogel for alleviating IVDD in rats. Conclusion. DDIT4 is a key player in mediating pyroptosis and IVDD in NPCs through the ROS-TXNIP-NLRP3 axis. Additionally, siDDIT4@G5-P-HA hydrogel has been found to relieve IVDD in rats. Our research offers an innovative treatment option for IVDD. Cite this article: Bone Joint Res 2024;13(5):247–260