Histological and reference system for the analysis of mouse intervertebral disc

BQU57 suppresses IL-1β-induced apoptosis and extracellular matrix degradation in nucleus pulposus cells by blocking the NF-κB signaling pathway

BACKGROUND

Intervertebral disc degeneration (IVDD) is a significant contributor to lower back pain (LBP), affecting approximately 80 % of the global population. The RalA inhibitor BQU57 plays a role in various cellular functions; however, its impact on nucleus pulposus cell (NPC) degeneration remains unclear.

METHODS

This study employed a combination of bioinformatics analysis and experimental validation to investigate the role of RalA in IVDD and its inhibitor BQU57 in its therapeutic potential. Gene expression datasets from the GEO database were analyzed to identify genes associated with IVDD, and clinical intervertebral disc samples were collected to validate the upregulation of RalA in degenerated discs. In vivo and in vitro assessments were conducted to evaluate the effects of BQU57 on the extracellular matrix (ECM) metabolism and apoptosis of nucleus pulposus (NP) cells.

RESULTS

Elevated expression of RalA was observed in degenerated intervertebral discs from IVDD patients, and its expression was correlated with disease severity. Further mechanistic studies revealed that the RalA inhibitor BQU57 could balance ECM metabolism and apoptosis, potentially through the activation of the NF-κB signaling pathway.

CONCLUSION

RalA plays a significant role in the pathogenesis of IVDD, and it may serve as a novel therapeutic target for IVDD. BQU57 demonstrates potential as an effective small molecule drug for the prevention and treatment of IVDD.

The BATF2-ATF3 axis exacerbates intervertebral disc degeneration via inducing mitochondrial dysfunction

Intervertebral disc degeneration (IVDD) is the leading cause of low back pain, spinal instability, disc herniation and spinal stenosis, which is a serious risk to human health, yet its molecular mechanisms remain unknown. The basic leucine zipper ATF-like transcription factor 2 (BATF2) has been reported to play important roles in regulating cell proliferation, apoptosis, and inflammatory responses; however, its specific role in IVDD remains unknown. We firstly demonstrated BATF2 expression was significantly upregulated in degenerated nucleus pulposus (NP) tissues. Functional assays demonstrated that BATF2 overexpression promoted nucleus pulposus cell (NPC) apoptosis and extracellular matrix (ECM) catabolism in vitro and vivo. It is further demonstrated that BATF2 impairs mitochondrial function by disturbing mitochondrial redox homeostasis. Mechanistically, BATF2 stabilizes the activating transcription factor 3 (ATF3) by inhibiting the ubiquitination modification of ATF3. Notably, ATF3 overexpression accelerated NPC apoptosis and ECM degradation. More importantly, ATF3 knockdown reversed the effects of BATF2-induced mitochondrial dysfunction and IVDD progression. These results suggest that BATF2-ATF3 axis disrupts mitochondrial redox homeostasis to impair mitochondrial function, thereby exacerbating the progression of IVDD. Targeting BATF2-ATF3 axis could provide a potential strategy for IVDD treatment.

Upregulated CEMIP promotes intervertebral disc degeneration via AP-1-mediated change in chromatin accessibility

BACKGROUND

Intervertebral disc degeneration (IDD), a chronic and multifactorial skeletal disorder, is the primary cause of low back pain. It results in reduced disc height and nucleus pulposus hydration due to proteoglycan loss and nucleus pulposus cells (NPCs) dysfunction within a hypoxic microenvironment. Metabolic dysregulation initiates catabolic processes, leading to extracellular matrix (ECM) degradation and compromising disc biomechanical integrity. Emerging evidence highlights epigenetic modifications as pivotal in IDD, influencing NPC gene expression transcriptionally and post-transcriptionally.

METHODS

In order to understand the epigenetic underpinnings of IDD, our study provided a comprehensive profile of chromatin accessibility changes in degenerated NPCs using Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC-seq).

RESULTS

With motif enrichment analysis, we identified the activator protein-1 (AP-1) transcription factor critical in driving the chromatin accessibility changes during IDD. Integrative ATAC-seq and transcriptional profiling revealed cell migration-inducing protein (CEMIP) as a key biomarker and contributor to IDD, exhibiting marked upregulation in IDD. Furthermore, we demonstrated that the AP-1 family, especially, c-Fos, orchestrates the upregulation of CEMIP. Elevated CEMIP plasma levels correlated with clinical IDD severity, and CEMIP knockout mice demonstrated improved IDD.

CONCLUSIONS

Mechanistically, CEMIP disrupted ECM homeostasis through its regulation of high molecular weight hyaluronic acid (HMW-HA) degradation, and its contribution to fibrotic changes. Our findings highlight CEMIP's vital role in IDD and identify the AP-1 family as a critical regulator of IDD, providing new potential therapeutic targets for novel IDD interventions.

KEY POINTS

Integrative ATAC-seq and transcriptional profiling revealed CEMIPas a key biomarker and contributor to IDD, exhibiting marked upregulation in IDD. Further, we demonstrated that the AP-1 family, especially, c-Fos, orchestrates the upregulation of CEMIP. Elevated CEMIP plasma levels correlated with clinical IDD severity, and CEMIP knockout mice demonstrated improved IDD. Mechanistically, CEMIP disrupted extracellular matrix homeostasis through its regulation of high molecular weight hyaluronic acid degradation, and its contribution to fibrotic changes. Our findings offer new avenues for IDD treatment strategies, with the potential to alleviate the global burden of back pain.

Transcription factor EP300 targets SIRT5 to promote autophagy of nucleus pulposus cells and attenuate intervertebral disc degeneration

BACKGROUND

Intervertebral disc degeneration (IVDD) is a prevalent spinal ailment and the leading cause of chronic low back pain. Understanding the exact pathogenesis of IVDD and developing targeted molecular drugs will be important in the future. Autophagy plays a key role in the metabolic processes and in the quality control of proteins in IVDD. However, the role of autophagy in the senescence of nucleus pulposus cell (NPC), the primary cells in the intervertebral disc responsible for maintaining the disc's structure and function, is not yet clear.

METHODS

Gene expression profiling data of human disc tissue were obtained from the Gene Expression Omnibus GSE15227, GSE23130, and GSE70362 datasets. Autophagy-related differentially expressed genes were identified from the Molecular Signatures Database (MSigDB) database. Weighted gene co-expression network analysis (WGCNA), receiver operating characteristic (ROC) curves, and least absolute shrinkage and selection operator (LASSO) regression identified an autophagy-related hub gene that encodes the E1A binding protein EP300 transcription factor in IVDD samples. Potential downstream target genes of EP300 were identified by bioinformatics analysis. The analysis identified sirtuin 5 (SIRT5) as a potential downstream target of EP300. Chromatin immunoprecipitation (ChIP)-qPCR, small interfering RNA (siRNA), and luciferase reporter gene assays were used to verify the interaction of EP300 and SIRT5 in vitro. For in vivo experiments, SIRT5 knockout mice and SIRT5-overexpressing adeno-associated virus serotype 5 (AAV5) were constructed to verify the effect of the EP300-SIRT5 signal axis on the progression of IVDD.

RESULTS

EP300 expression was reduced in the IVDD samples compared with its expression in healthy disc tissue samples. The reduced EP300 expression inhibited the occurrence of autophagy, which promoted NPC senescence. ChIP-qPCR and luciferase reporter gene assays showed that EP300 promoted SIRT5 expression by direct binding to its promoter. Activation of EP300 expression increased SIRT5 expression and significantly improved autophagy for inhibition of NPC senescence. In vivo experiments confirmed that knockdown of EP300 promoted NPC senescence and led to an exacerbation of IVDD, which was reversed by SIRT5 overexpression.

CONCLUSION

Our results provide the first evidence for the importance of EP300 and SIRT5 interactions in promoting IVDD development by inhibiting autophagy during IVDD. The EP300-SIRT5 signaling axis was identified as a promising target for therapy of IVDD based on autophagy genes.

M2 macrophages regulate nucleus pulposus cell extracellular matrix synthesis through the OPN-CD44 axis in intervertebral disc degeneration

OBJECTIVE

Macrophages play a crucial role in various physiological processes. In intervertebral disc degeneration (IDD), macrophage infiltration has been observed in human intervertebral disc (IVD) specimens, but how macrophages influence IDD remains unclear.

METHODS

According to the single-cell transcriptome expression profiles from GSE165722, we verified the infiltration of macrophages in IDD and the possible interaction between infiltrated macrophages and nucleus pulposus cells (NPCs). The expression of macrophage-associated markers was verified in specimens of human nucleus pulposus, lumbar spinal instability mice and annulus fibrosus puncture mice. By treating NPCs cocultured with M2 macrophages with osteopontin (OPN) neutralization antibody and siCD44, we demonstrated that both in vitro and in vivo macrophages regulated IDD through the OPN-CD44 axis. Using transforming growth factor beta 1 and siCD44 treatment, we verified that CD44 regulated the pSMAD2/3 pathway.

RESULTS

IDD engaged macrophage infiltration, mainly gathered in the endplate, and induced macrophage M2 polarization. Infiltrated macrophages showed high-level expression of OPN, and NPCs showed upregulated CD44. Depletion of macrophages significantly decreased the expression of OPN and CD44 in degenerative IVD, concurrently exacerbating IDD. The co-culture of macrophages and NPCs in vitro demonstrated that the conditioned media from NPCs induced macrophage M2 polarization. Further, M2 macrophages rescued NPCs extracellular matrix (ECM) phenotype through the OPN-CD44 axis, by regulating pSMAD2/3 nuclear translocation.

CONCLUSIONS

Our findings suggest that macrophages regulate NPC ECM expression in IDD through the OPN-CD44 axis, emphasizing the therapeutic potential of targeting macrophages and the OPN-CD44 axis for IDD prevention and treatment.

Meteorin-like protein alleviates intervertebral disc degeneration by suppressing lipid accumulation in nucleus pulposus cells via PPARα-CPT1A activation

Disturbances in lipid metabolism are closely related to intervertebral disc degeneration (IDD). However, the lipid metabolism characteristics of nucleus pulposus (NP) cells during IDD are unclear. Exercise protects against IDD and acts as a potent mediator of organ metabolism, in which muscle-secreted myokines actively participate. However, whether exercise-induced myokines alleviate IDD by regulating lipid metabolism in NP cells remains unknown. The present study revealed that lipid accumulation is the metabolic reprogramming phenotype in NP cells during IDD, which was attributed to an imbalance between increased fatty acid/triglyceride synthesis and diminished utilization, and was further associated with extracellular matrix (ECM) degradation and cell senescence. To explore the interaction between exercise and IDD, Sprague-Dawley rats were subjected to five weeks of treadmill running exercise, and rats in the exercise group exhibited less severe IDD than did those in the sedentary group. The expression of meteorin-like protein (Metrnl), a newly-discovered myokine that participates in lipid metabolism regulation, was observed to increase in muscle, serum and NP tissue after exercise. Moreover, Metrnl ameliorated lipid accumulation in NP cells and further alleviated ECM degradation and cell senescence. Mechanistically, Metrnl activated the fatty acid β-oxidation rate-limiting enzyme carnitine palmitoyltransferase 1A (CPT1A) via peroxisome proliferator-activated receptor α (PPARα) to increase lipid utilization in NP cells. This study provides insight into the lipid metabolic features of NP cells in IDD and reveals the intrinsic connections among exercise, metabolism and IDD, with the myokine Metrnl emerging as a pivotal mediator with therapeutic potential.

HMGB1-mediated macrophage regulation of NF-κB activation and MMP3 upregulation in nucleus pulposus cells: A critical mechanism in the vicious cycle of intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is a leading cause of low back pain, primarily driven by inflammatory processes within the disc, particularly involving the infiltration and activity of macrophages. High Mobility Group Box 1 (HMGB1) has been identified as a crucial mediator in this inflammatory cascade, yet its precise role in macrophage-induced disc degeneration remains unclear. In this study, we employed a combination of in vivo and in vitro models, including genetically engineered mice with macrophage-specific overexpression of HMGB1, a rat model of IVDD, and cultured macrophages and nucleus pulposus cells (NPCs), to elucidate the role of HMGB1 in IVDD. Our findings reveal that HMGB1 overexpression in macrophages significantly accelerates IVDD progression by enhancing NF-κB activation and upregulating MMP3 expression in NPCs. Furthermore, the administration of glycyrrhizin (GL), an HMGB1 inhibitor, effectively mitigated these effects, delaying IVDD progression. This study not only uncovers the critical mechanisms by which HMGB1 regulates the interactions between macrophages and NPCs in the inflammatory microenvironment but also provides a theoretical framework for targeting HMGB1 as a potential therapeutic strategy for IVDD. Thus, our findings suggest a promising novel approach for the treatment of this condition.

Matrix stiffness regulates nucleus pulposus cell glycolysis by MRTF-A-dependent mechanotransduction

Increased matrix stiffness of nucleus pulposus (NP) tissue is a main feature of intervertebral disc degeneration (IVDD) and affects various functions of nucleus pulposus cells (NPCs). Glycolysis is the main energy source for NPC survival, but the effects and underlying mechanisms of increased extracellular matrix (ECM) stiffness on NPC glycolysis remain unknown. In this study, hydrogels with different stiffness were established to mimic the mechanical environment of NPCs. Notably, increased matrix stiffness in degenerated NP tissues from IVDD patients was accompanied with impaired glycolysis, and NPCs cultured on rigid substrates exhibited a reduction in glycolysis. Meanwhile, RNA sequencing analysis showed altered cytoskeleton-related gene expression in NPCs on rigid substrates. Myocardin-related transcription factor A (MRTF-A) is a transcriptional coactivator in mechanotransduction mainly responding to cytoskeleton remodeling, which was activated and translocated to the nucleus under rigid substrate and was upregulated during IVDD progression. Furthermore, gas chromatography-mass spectrometry (GC-MS) analysis revealed that MRTF-A overexpression reduced NPC glycolytic metabolite abundance and identified a correlation with AMPK pathway. Mechanistically, rigid substrates and MRTF-A overexpression inhibited Kidins220 expression and AMPK phosphorylation in NPCs, whereas MRTF-A inhibition, treated with the MRTF-A inhibitor CCG, partially rescued NP tissue degeneration and glycolytic enzyme expression. Our data demonstrate that MRTF-A is a critical regulator that responds to increased matrix stiffness in IVDD, and MRTF-A activation reduces NPC glycolysis by down-regulating Kidins220 and inhibiting AMPK phosphorylation.

Rejuvenation Modulation of Nucleus Pulposus Progenitor Cells Reverses Senescence-Associated Intervertebral Disc Degeneration

The decreased regeneration potential of aging nucleus pulposus resident progenitor cells (NPPCs) fails to resist intervertebral disc degeneration (IVDD), and strategies to remodel the regeneration capacity of senescent NPPC are urgently needed. A decrease in Klotho gene expression in NPPCs of both old mice and humans exacerbates the impaired regenerative functionality of NPPC. Here, an NPPC-targeted lipid thymine nanoparticle (NT-LNP) is reported for the in situ manipulation of the regenerative repair potential of NPPCs, restoration of degenerated nucleus pulposus tissue, and mitigation of IVDD. Specifically, the results showed that the in-house customized lipid nanoparticles efficiently introduced Klotho circular ribonucleic acid (circRNA) into NPPCs to engender a renascent phenotype and tuned the balance of extracellular matrix synthesis/catabolism in vitro and in vivo. Moreover, an intradiscal injectable hydrogel system that scavenges chemokines (MCP1 and IL8) in tandem with NPPCs rejuvenated NT-LNPs in the IVD, modulating the inflammatory environment and synergistically promoting the regeneration of degenerated intervertebral discs. In summary, the findings establish that NPPCs can be re-engineered to be youthful and pluripotent to maintain homeostasis and rejuvenation, thereby providing a reversible treatment strategy for IVDD with broad application in other senescence-related diseases.

Fibrocyte enrichment and myofibroblastic adaptation causes nucleus pulposus fibrosis and associates with disc degeneration severity

Fibrotic remodeling of nucleus pulposus (NP) leads to structural and mechanical anomalies of intervertebral discs that prone to degeneration, leading to low back pain incidence and disability. Emergence of fibroblastic cells in disc degeneration has been reported, yet their nature and origin remain elusive. In this study, we performed an integrative analysis of multiple single-cell RNA sequencing datasets to interrogate the cellular heterogeneity and fibroblast-like entities in degenerative human NP specimens. We found that disc degeneration severity is associated with an enrichment of fibrocyte phenotype, characterized by CD45 and collagen I dual positivity, and expression of myofibroblast marker α-smooth muscle actin. Refined clustering and classification distinguished the fibrocyte-like populations as subtypes in the NP cells - and immunocytes-clusters, expressing disc degeneration markers HTRA1 and ANGPTL4 and genes related to response to TGF-β. In injury-induced mouse disc degeneration model, fibrocytes were found recruited into the NP undergoing fibrosis and adopted a myofibroblast phenotype. Depleting the fibrocytes in CD11b-DTR mice in which myeloid-derived lineages were ablated by diphtheria toxin could markedly attenuate fibrous modeling and myofibroblast formation in the NP of the degenerative discs, and prevent disc height loss and histomorphological abnormalities. Marker analysis supports that disc degeneration progression is dependent on a function of CD45+COL1A1+ and αSMA+ cells. Our findings reveal that myeloid-derived fibrocytes play a pivotal role in NP fibrosis and may therefore be a target for modifying disc degeneration and promoting its repair.

Tomatidine Alleviates Intervertebral Disc Degeneration by Activating the Nrf2/HO-1/GPX4 Signaling Pathway

Purpose

Intervertebral disc degeneration (IDD) is a leading cause of low back pain, and developing new molecular drugs and targets for IDD is a new direction for future treatment strategies. The aim of this study is to investigate the effects and mechanisms of tomatidine in ameliorating lumbar IDD.

Methods

Nucleus pulposus cells (NPCs) exposed to lipopolysaccharides were used as an in vitro model to investigate changes in the expression of extracellular matrix components and associated signaling pathway molecules. A lumbar instability model was used to simulate IDD. Tomatidine (Td) was then administered intraperitoneally, and its effects were evaluated through histopathological analysis.

Results

In vitro, Td significantly promoted ECM anabolism, inhibited ECM catabolism, and reduced oxidative stress and ferroptosis in LPS-stimulated NPCs. When Nrf2 expression was inhibited, oxidative stress and ferroptosis were exacerbated, and the protective effects of Td on NPCs were lost, suggesting the Nrf2/HO-1/GPX4 axis is critical for the therapeutic effects of Td. In vivo, histopathological analysis demonstrated that Td ameliorated IDD in a murine model.

Conclusion

Td alleviates IDD in vitro and in vivo by activating the Nrf2/HO-1/GPX4 pathway to inhibit ferroptosis in NPCs. This mechanism suggests Td is a promising candidate for IDD treatment.

Network pharmacology and experimental validation to reveal the pharmacological mechanisms of Astragaloside Ⅳ in treating intervertebral disc degeneration

This study aims to identify potential targets and regulatory mechanisms of Astragaloside Ⅳ (AS-Ⅳ) in treating intervertebral disc degeneration (IDD) through network pharmacology analysis with experimental validation. Lumbar spine instability (LSI) mouse models were first established and treated with AS-Ⅳ. Micro-CT, safranin O-fast green staining, IDD score, RT-PCR and immunohistochemistry staining were employed to demonstrate the effect of AS-Ⅳ. Network pharmacology was used to predict the signaling pathways and potential targets of AS-Ⅳ in treating IDD. RT-PCR and immunohistochemistry staining were used to elucidate and validate the mechanism of AS-Ⅳ in vivo. Animal experiments showed that AS-Ⅳ maintained disc height and volume, improved matrix metabolism in LSI mice, and restored Col2α1, ADAMTS-5, Aggrecan, and MMP-13 expression in degenerated discs. Network pharmacology analysis identified 32 cross-targets between AS-Ⅳ and IDD, and PPI network analysis filtered out 11 core genes, including ALB, MAPK1, MAPK14 (p38 MAPK), EGFR, TGFBR1, MAPK8, MMP3, ANXA5, ESR1, CASP3, and IGF1. Enrichment analysis revealed that 7 of the 11 core target genes enriched in the MAPK signaling pathway, and AS-Ⅳ exhibited stable binding to them according to molecular docking results. Experimental validation indicated that AS-Ⅳ reversed mRNA levels of 7 core targets in degenerated disc tissues in LSI mice. Immunohistochemistry staining further revealed that AS-Ⅳ treatment mainly depressed IDD-elevated protein levels of EGFR, p38 MAPK and CASP3 in the annulus fibrosus. This study elucidates that AS-Ⅳ alleviates lumbar spine instability-induced IDD in mice, suggesting the mechanism may involve inhibition of the EGFR/MAPK signaling pathway.

PRDM1 promotes nucleus pulposus cell pyroptosis leading to intervertebral disc degeneration via activating CASP1 transcription

Intervertebral disc degeneration (IVDD) is a primary contributor to low back pain and poses a considerable burden to society. However, the molecular mechanisms underlying IVDD remain to be elucidated. PR/SET domain 1 (PRDM1) regulates cell proliferation, apoptosis, and inflammatory responses in various diseases. Despite these regulatory functions, the mechanism of action of PRDM1 in IVDD remains unexplored. In this study, we investigated the role and underlying mechanisms of action of PRDM1 in IVDD progression. The expression of PRDM1 in nucleus pulposus (NP) tissues and NP cells (NPCs) was assessed using western blotting, immunohistochemistry, and immunofluorescence. The effects of PRDM1 on IVDD progression were investigated in vitro and in vivo. Mechanistically, mRNA sequencing, chromatin immunoprecipitation, and dual-luciferase reporter assays were performed to confirm that PRDM1 triggered CASP1 transcription. Our study demonstrated for the first time that PRDM1 expression was substantially upregulated in degenerated NP tissues and NPCs. PRDM1 overexpression promoted NPCs pyroptosis by inhibiting mitophagy and exacerbating IVDD progression, whereas PRDM1 silencing exerted the opposite effect. Furthermore, PRDM1 activated CASP1 transcription, thereby promoting NPCs pyroptosis in vitro. Notably, CASP1 silencing reversed the effects of PRDM1 on the NPCs. To the best of our knowledge, this study is the first to demonstrate that PRDM1 silencing inhibits NPCs pyroptosis by repressing CASP1 transcription, which may be a promising new therapeutic target for IVDD.

Magnetic resonance imaging classification in a percutaneous needle injury rat model of intervertebral disc degeneration

BACKGROUND

During the development of disease-modifying intervertebral disc degeneration (IDD) drugs, the rat model of IDD is frequently used for disease progression assessment. The aim of this study was to describe a magnetic resonance (MRI) scoring system for the assessment of different disc conditions in puncture-induced IDD, allowing standardization and comparison of results obtained by different investigators.

METHODS

A total of 36 Sprague-Dawley rats were utilized in the present study. The animals were divided into two groups: a sham group and an IDD group caused by puncture. The rats in the IDD group were subsequently divided into six categories based on time frames, with five rats in each category. The sham group was divided into two sub-groups (n = 3) for 28 and 56 days, respectively. T2-weighted images of rats consecutively studied with MRI of the coccygeal discs were classified according to the time course using the corresponding histological data. Additional scoring of the micro-CT was employed to identify the progression of bone destruction of the rat model of IDD.

RESULTS

A comparison of the MRI results between the sham group and the IDD group revealed a significant reduction in NP height, area, T2WI value, and DHI in the latter group (P < 0.05). The micro-CT results demonstrated that following acupuncture, there was a notable decline in the BV, Tb.N, and height of the coccygeal vertebra, while the BS/BV and Tb.Sp exhibited a significant increase (P < 0.05). The histological results were analogous to the MRI results, indicating a progressive exacerbation of IDD and a corresponding increase in NP score (P < 0.05). The results of the MRI were found to be consistent with those of the micro-CT and histological analyses (P < 0.05). The results of the study demonstrate a robust correlation between MRI analysis and histological findings. Live animals are employed for MRI analysis to improve experiment comparability. The reliability of the MRI scoring system ensures assessment of disease progression in live animals, while promoting cost savings and animal welfare by avoiding the sacrifice of animals at different times.

CONCLUSIONS

The described scoring paradigm has quantitatively been found to differentiate IDD disease progression in an in vivo rat model. Hence, we suggest employing it to evaluate the rat IDD model and assess the effects of treatments in this model.

Identification and validation of ferroptosis-related biomarkers in intervertebral disc degeneration

Introduction

Ferroptosis plays a significant role in intervertebral disc degeneration (IDD). Understanding the key genes regulating ferroptosis in IDD could reveal fundamental mechanisms of the disease, potentially leading to new diagnostic and therapeutic targets.

Methods

Public datasets (GSE23130 and GSE70362) and the FerrDb database were analyzed to identify ferroptosis-related genes (DE-FRGs) involved in IDD. Single-cell RNA sequencing data (GSE199866) was used to validate the specific roles and expression patterns of these genes. Immunohistochemistry and Western blot analyses were subsequently conducted in both clinical samples and mouse models to assess protein expression levels across different tissues.

Results

The analysis identified seven DE-FRGs, including MT1G, CA9, AKR1C1, AKR1C2, DUSP1, CIRBP, and KLHL24, with their expression patterns confirmed by single-cell RNA sequencing. Immunohistochemistry and Western blot analysis further revealed that MT1G, CA9, AKR1C1, AKR1C2, DUSP1, and KLHL24 exhibited differential expression during the progression of IDD. Additionally, the study highlighted the potential immune-modulatory functions of these genes within the IDD microenvironment.

Discussion

Our study elucidates the critical role of ferroptosis in IDD and identifies specific genes, such as MT1G and CA9, as potential targets for diagnosis and therapy. These findings offer new insights into the molecular mechanisms underlying IDD and present promising avenues for future research and clinical applications.

A novel spherical GelMA-HAMA hydrogel encapsulating APET×2 polypeptide and CFIm25-targeting sgRNA for immune microenvironment modulation and nucleus pulposus regeneration in intervertebral discs

METHODS

Single-cell transcriptomics and high-throughput transcriptomics were used to screen factors significantly correlated with intervertebral disc degeneration (IDD). Expression changes of CFIm25 were determined via RT-qPCR and Western blot. NP cells were isolated from mouse intervertebral discs and induced to degrade with TNF-α and IL-1β. CFIm25 was knocked out using CRISPR-Cas9, and CFIm25 knockout and overexpressing nucleus pulposus (NP) cell lines were generated through lentiviral transfection. Proteoglycan expression, protein expression, inflammatory factor expression, cell viability, proliferation, migration, gene expression, and protein expression were analyzed using various assays (alcian blue staining, immunofluorescence, ELISA, CCK-8, EDU labeling, transwell migration, scratch assay, RT-qPCR, Western blot). The GelMA-HAMA hydrogel loaded with APET×2 polypeptide and sgRNA was designed, and its effects on NP regeneration were assessed through in vitro and mouse model experiments. The progression of IDD in mice was evaluated using X-ray, H&E staining, and Safranin O-Fast Green staining. Immunohistochemistry was performed to determine protein expression in NP tissue. Proteomic analysis combined with in vitro and in vivo experiments was conducted to elucidate the mechanisms of hydrogel action.

RESULTS

CFIm25 was upregulated in IDD NP tissue and significantly correlated with disease progression. Inhibition of CFIm25 improved NP cell degeneration, enhanced cell proliferation, and migration. The hydrogel effectively knocked down CFIm25 expression, improved NP cell degeneration, promoted cell proliferation and migration, and mitigated IDD progression in a mouse model. The hydrogel inhibited inflammatory factor expression (IL-6, iNOS, IL-1β, TNF-α) by targeting the p38/NF-κB signaling pathway, increased collagen COLII and proteoglycan Aggrecan expression, and suppressed NP degeneration-related factors (COX-2, MMP-3).

CONCLUSION

The study highlighted the crucial role of CFIm25 in IDD and introduced a promising therapeutic strategy using a porous spherical GelMA-HAMA hydrogel loaded with APET×2 polypeptide and sgRNA. This innovative approach offers new possibilities for treating degenerated intervertebral discs.

Nrf2 activation by pyrroloquinoline quinone inhibits natural aging-related intervertebral disk degeneration in mice

Age-related intervertebral disk degeneration (IVDD) involves increased oxidative damage, cellular senescence, and matrix degradation. Pyrroloquinoline quinone (PQQ) is a water-soluble vitamin-like compound with strong anti-oxidant capacity. The goal of this study was to determine whether PQQ can prevent aging-related IVDD, and the underlying mechanism. Here, we found that dietary PQQ supplementation for 12 months alleviated IVDD phenotypes in aged mice, including increased disk height index and reduced histological scores and cell loss, without toxicity. Mechanistically, PQQ inhibited oxidative stress, cellular senescence, and senescence-associated secretory phenotype (SASP) in the nucleus pulposus and annulus fibrosus of aged mice. Similarly, PQQ protected against interleukin-1β-induced matrix degradation, reactive oxygen species accumulation, and senescence in human nucleus pulposus cells (NPCs) in vitro. Molecular docking predicted and biochemical assays validated that PQQ interacts with specific residues to dissociate the Keap1-Nrf2 complex, thereby increasing nuclear Nrf2 translocation and activation of Nrf2-ARE signaling. RNA sequencing and luciferase assays revealed Nrf2 can transcriptionally upregulate Wnt5a by binding to its promoter, while Wnt5a knockdown prevented PQQ inhibition of matrix metalloproteinase-13 in NPCs. Notably, PQQ supplementation failed to alleviate aging-associated IVDD phenotypes and oxidative stress in aged Nrf2 knockout mice, indicating Nrf2 is indispensable for PQQ bioactivities. Collectively, this study demonstrates Nrf2 activation by PQQ inhibits aging-induced IVDD by attenuating cellular senescence and matrix degradation. This study clarifies Keap1-Nrf2-Wnt5a axis as the novel signaling underlying the protective effects of PQQ against aging-related IVDD, and provides evidence for PQQ as a potential agent for clinical prevention and treatment of natural aging-induced IVDD.

Pannexin 3 deletion in mice results in knee osteoarthritis and intervertebral disc degeneration after forced treadmill running

Pannexin 3 (Panx3) is a glycoprotein that forms mechanosensitive channels expressed in chondrocytes and annulus fibrosus cells of the intervertebral disc (IVD). Evidence suggests Panx3 plays contrasting roles in traumatic versus aging osteoarthritis (OA) and intervertebral disc degeneration (IDD). However, whether its deletion influences the response of joint tissue to forced use is unknown. The purpose of this study was to determine if Panx3 deletion in mice causes increased knee joint OA and IDD after forced treadmill running. Male and female wildtype (WT) and Panx3 knockout (KO) mice were randomized to either a no-exercise group (sedentary; SED) or daily forced treadmill running (forced exercise; FEX) from 24 to 30 weeks of age. Knee cartilage and IVD histopathology were evaluated by histology, while tibial secondary ossification centers were analyzed using microcomputed tomography (µCT). Both male and female Panx3 KO mice developed larger superficial defects of the tibial cartilage after forced treadmill running compared with SED WT mice. Additionally, Panx3 KO mice developed reduced bone volume, and female PANX3 KO mice had lengthening of the lateral tubercle at the intercondylar eminence. In the lower lumbar spine, both male and female Panx3 KO mice developed histopathological features of IDD after running compared to SED WT mice. These findings suggest that the combination of deleting Panx3 and forced treadmill running induces OA and causes histopathological changes associated with the degeneration of the IVDs in mice.

Progenitor-like cells contributing to cellular heterogeneity in the nucleus pulposus are lost in intervertebral disc degeneration

The nucleus pulposus (NP) in the intervertebral disc (IVD) arises from embryonic notochord. Loss of notochordal-like cells in humans correlates with onset of IVD degeneration, suggesting that they are critical for healthy NP homeostasis and function. Comparative transcriptomic analyses identified expression of progenitor-associated genes (GREM1, KRT18, and TAGLN) in the young mouse and non-degenerated human NP, with TAGLN expression reducing with aging. Lineage tracing using Tagln-CreERt2 mice identified peripherally located proliferative NP (PeriNP) cells in developing and postnatal NP that provide a continuous supply of cells to the entire NP. PeriNP cells were diminished in aged mice and absent in puncture-induced degenerated discs. Single-cell transcriptomes of postnatal Tagln-CreERt2 IVD cells indicate enrichment for TGF-β signaling in Tagln descendant NP sub-populations. Notochord-specific removal of TGF-β/BMP mediator Smad4 results in loss of Tagln+ cells and abnormal NP morphologies. We propose Tagln+ PeriNP cells are potential progenitors crucial for NP homeostasis.

Nuclear factor κB overactivation in the intervertebral disc leads to macrophage recruitment and severe disc degeneration

Persistent inflammation has been associated with severe disc degeneration (DD). This study investigated the effect of prolonged nuclear factor κB (NF-κB) activation in DD. Using an inducible mouse model, we genetically targeted cells expressing aggrecan, a primary component of the disc extra cellular matrix, for activation of the canonical NF-κB pathway. Prolonged NF-κB activation led to severe structural degeneration accompanied by increases in gene expression of inflammatory molecules (Il1b, Cox2, Il6, and Nos2), chemokines (Mcp1 and Mif), and catabolic enzymes (Mmp3, Mmp9, and Adamts4). Increased recruitment of proinflammatory (F4/80+,CD38+) and inflammatory resolving (F4/80+,CD206+) macrophages was observed within caudal discs. We found that the secretome of inflamed caudal disc cells increased macrophage migration and inflammatory activation. Lumbar discs did not exhibit phenotypic changes, suggestive of regional spinal differences in response to inflammatory genetic overactivation. Results suggest prolonged NF-κB activation can induce severe DD through increases in inflammatory cytokines, chemotactic proteins, catabolic enzymes, and the recruitment and activation of macrophage cell populations.

A Narrative Review of the Roles of Chondromodulin-I (Cnmd) in Adult Cartilage Tissue

Articular cartilage is crucial for joint function but its avascularity limits intrinsic repair, leading to conditions like osteoarthritis (OA). Chondromodulin-I (Cnmd) has emerged as a key molecule in cartilage biology, with potential implications for OA therapy. Cnmd is primarily expressed in cartilage and plays an important role in chondrocyte proliferation, cartilage homeostasis, and the blocking of angiogenesis. In vivo and in vitro studies on Cnmd, also suggest an involvement in bone repair and in delaying OA progression. Its downregulation correlates with OA severity, indicating its potential as a therapeutic target. Further research is needed to fully understand the mode of action of Cnmd and its beneficial implications for managing OA. This comprehensive review aims to elucidate the molecular characteristics of Cnmd, from its expression pattern, role in cartilage maintenance, callus formation during bone repair and association with OA.

Intervertebral disc-intrinsic Hedgehog signaling maintains disc cell phenotypes and prevents disc degeneration through both cell autonomous and non-autonomous mechanisms

Intervertebral disc degeneration is closely related to abnormal phenotypic changes in disc cells. However, the mechanism by which disc cell phenotypes are maintained remains poorly understood. Here, Hedgehog-responsive cells were found to be specifically localized in the inner annulus fibrosus and cartilaginous endplate of postnatal discs, likely activated by Indian Hedgehog. Global inhibition of Hedgehog signaling using a pharmacological inhibitor or Agc1-CreERT2-mediated deletion of Smo in disc cells of juvenile mice led to spontaneous degenerative changes in annulus fibrosus and cartilaginous endplate accompanied by aberrant disc cell differentiation in adult mice. In contrast, Krt19-CreER-mediated deletion of Smo specifically in nucleus pulposus cells led to healthy discs and normal disc cell phenotypes. Similarly, age-related degeneration of nucleus pulposus was accelerated by genetic inactivation of Hedgehog signaling in all disc cells, but not in nucleus pulposus cells. Furthermore, inactivation of Gli2 in disc cells resulted in partial loss of the vertebral growth plate but otherwise healthy discs, whereas deletion of Gli3 in disc cells largely corrected disc defects caused by Smo ablation in mice. Taken together, our findings not only revealed for the first time a direct role of Hedgehog-Gli3 signaling in maintaining homeostasis and cell phenotypes of annuls fibrosus and cartilaginous endplate, but also identified disc-intrinsic Hedgehog signaling as a novel non-cell-autonomous mechanism to regulate nucleus pulposus cell phenotype and protect mice from age-dependent nucleus pulposus degeneration. Thus, targeting Hedgehog signaling may represent a potential therapeutic strategy for the prevention and treatment of intervertebral disc degeneration.

CCR2 monocytes as therapeutic targets for acute disc herniation and radiculopathy in mouse models

OBJECTIVE

Back pain and radiculopathy caused by disc herniation are major health issues worldwide. While macrophages are key players in disc herniation induced inflammation, their roles and origins in disease progression remain unclear. We aim to study the roles of monocytes and derivatives in a mouse model of disc herniation.

METHODS

Using a CCR2-CreER; R26R-EGFP (Ai6) transgenic mouse strain, we fate-mapped C-C chemokine receptor type 2 (CCR2) expressing monocytes and derivatives at disc herniation sites, and employed a CCR2RFP/RFP mouse strain and a CCR2-specific antagonist to study the effects of CCR2+ monocytes on local inflammatory responses, pain level, and disc degeneration by immunostaining, flow cytometry, and histology.

RESULTS

CCR2+ monocytes (GFP+) increased at the sites of disc hernia over postoperative day 4, 6, and 9 in CCR2-CreER; Ai6 mice. F4/80+ cells increased, and meanwhile, CD11b+ cells trended downward. Co-localization analysis revealed that both GFP+CD11b+ and GFP+F4/80+ constituted the majority of CD11b+ and F4/80+ cells at disc hernia sites. Fluorescence activated cell sorter purified GFP+ cells exhibited higher cytokine expressions than GFP- cells. Inhibition of CCR2 signaling reduced infiltration of monocytes and macrophages, alleviated pain, maintained disc height, and reduced osteoclast activity in adjacent cortical bone for up to 1 month.

CONCLUSION

Our findings suggest that circulating CCR2+ monocytes play important roles in initiating and promoting the local inflammatory responses, pain sensitization, and degenerative changes after disc herniation, and thus may serve as therapeutic targets for disc herniation induced back and leg pain.

Comparative histopathological analysis of age-associated intervertebral disc degeneration in CD-1 and C57BL/6 mice: Anatomical and sex-based differences

Background

Intervertebral disc (IVD) degeneration is a major contributor to back pain and disability. The cause of IVD degeneration is multifactorial, with no disease-modifying treatments. Mouse models are commonly used to study IVD degeneration; however, the effects of anatomical location, strain, and sex on the progression of age-associated degeneration are poorly understood.

Methods

A longitudinal study was conducted to characterize age-, anatomical-, and sex-specific differences in IVD degeneration in two commonly used strains of mice, C57BL/6 and CD-1. Histopathological evaluation of the cervical, thoracic, lumbar, and caudal regions of mice at 6, 12, 20, and 24 months of age was conducted by two blinded observers at each IVD for the nucleus pulposus (NP), annulus fibrosus (AF), and the NP/AF boundary compartments, enabling analysis of scores by tissue compartment, summed scores for each IVD, or averaged scores for each anatomical region.

Results

C57BL/6 mice displayed mild IVD degeneration until 24 months of age; at this point, the lumbar spine demonstrated the most degeneration compared to other regions. Degeneration was detected earlier in the CD-1 mice (20 months of age) in both the thoracic and lumbar spine. In CD-1 mice, moderate to severe degeneration was noted in the cervical spine at all time points assessed. In both strains, age-associated IVD degeneration in the thoracic and lumbar spine was associated with increased histopathological scores in all IVD compartments. In both strains, minimal degeneration was detected in caudal IVDs out to 24 months of age. Both C57BL/6 and CD-1 mice displayed sex-specific differences in the presentation and progression of age-associated IVD degeneration.

Conclusions

These results showed that the progression and severity of age-associated degeneration in mouse models is associated with marked differences based on anatomical region, sex, and strain. This information provides a fundamental baseline characterization for users of mouse models to enable effective and appropriate experimental design, interpretation, and comparison between studies.

Enhanced Intervertebral Disc Repair via Genetically Engineered Mesenchymal Stem Cells with Tetracycline Regulatory System

The therapeutic potential of Mesenchymal stem cells (MSCs) for the treatment of Intervertebral disc (IVD) degeneration can be enhanced by amplifying specific cytokines and proteins. This study aimed to investigate the therapeutic potential of tetracycline-off system-engineered tonsil-derived mesenchymal stem cells (ToMSC-Tetoff-TGFβ1-IGF1-BMP7) for treating intervertebral disc (IVD) degeneration. ToMSCs were isolated from a tonsillectomy patient and genetically modified with four distinct plasmids via CRISPR/Cas9-mediated knock-in gene editing. Transgene expression was confirmed through immunofluorescence, western blots, and an enzyme-linked immunosorbent assay for transforming growth factor beta 1 (TGFβ1) protein secretion, and the effect of MSC-TetOff-TGFβ1-IGF1-BMP7 on disc injury was assessed in a rat model. The ToMSC-Tetoff-TGFβ1-IGF1-BMP7 treatment exhibited superior therapeutic effects compared to ToMSC-TGFβ1, and ToMSC-SDF1α implantation groups, stimulating the regeneration of nucleus pulposus (NP) cells crucial for IVD. The treatment showed potential to restore the structural integrity of the extracellular matrix (ECM) by upregulating key molecules such as aggrecan and type II collagen. It also exhibited anti-inflammatory properties and reduced pain-inducing neuropeptides. ToMSC-Tetoff-TGFβ1-IGF1-BMP7 holds promise as a novel treatment for IVD degeneration. It appears to promote NP cell regeneration, restore ECM structure, suppress inflammation, and reduce pain. However, more research and clinical trials are required to confirm its therapeutic potential.

Loss of Pinch Proteins Causes Severe Degenerative Disc Disease-Like Lesions in Mice

Degenerative disc disease (DDD) is one of the most common skeletal disorders affecting aged populations. DDD is the leading cause of low back/neck pain, resulting in disability and huge socioeconomic burdens. However, the molecular mechanisms underlying DDD initiation and progression remain poorly understood. Pinch1 and Pinch2 are LIM-domain-containing proteins with crucial functions in mediating multiple fundamental biological processes, such as focal adhesion, cytoskeletal organization, cell proliferation, migration, and survival. In this study, we found that Pinch1 and Pinch2 were both highly expressed in healthy intervertebral discs (IVDs) and dramatically downregulated in degenerative IVDs in mice. Deleting Pinch1 in aggrecan-expressing cells and Pinch2 globally (AggrecanCreERT2; Pinch1fl/fl; Pinch2-/-) caused striking spontaneous DDD-like lesions in lumbar IVDs in mice. Pinch loss inhibited cell proliferation and promoted extracellular matrix (ECM) degradation and apoptosis in lumbar IVDs. Pinch loss markedly enhanced the production of pro-inflammatory cytokines, especially TNFα, in lumbar IVDs and exacerbated instability-induced DDD defects in mice. Pharmacological inhibition of TNFα signaling mitigated the DDD-like lesions caused by Pinch loss. In human degenerative NP samples, reduced expression of Pinch proteins was correlated with severe DDD progression and a markedly upregulated expression of TNFα. Collectively, we demonstrate the crucial role of Pinch proteins in maintaining IVD homeostasis and define a potential therapeutic target for DDD.

Phosphorylation of KRT8 (keratin 8) by excessive mechanical load-activated PKN (protein kinase N) impairs autophagosome initiation and contributes to disc degeneration

Excessive mechanical load (overloading) is a well-documented pathogenetic factor for many mechano stress-induced pathologies, i.e. intervertebral disc degeneration (IDD). Under overloading, the balance between anabolism and catabolism within nucleus pulposus (NP) cells are badly thrown off, and NP cells undergo apoptosis. However, little is known about how the overloading is transduced to the NP cells and contributes to disc degeneration. The current study shows that conditional knockout of Krt8 (keratin 8) within NP aggravates load-induced IDD in vivo, and overexpression of Krt8 endows NP cells greater resistance to overloading-induced apoptosis and degeneration in vitro. Discovery-driven experiments shows that phosphorylation of KRT8 on Ser43 by overloading activated RHOA-PKN (protein kinase N) impedes trafficking of Golgi resident small GTPase RAB33B, suppresses the autophagosome initiation and contributes to IDD. Overexpression of Krt8 and knockdown of Pkn1 and Pkn2, at an early stage of IDD, ameliorates disc degeneration; yet only knockdown of Pkn1 and Pkn2, when treated at late stage of IDD, shows a therapeutic effect. This study validates a protective role of Krt8 during overloading-induced IDD and demonstrates that targeting overloading activation of PKNs could be a novel and effective approach to mechano stress-induced pathologies with a wider window of therapeutic opportunity.Abbreviations: AAV: adeno-associated virus; AF: anulus fibrosus; ANOVA: analysis of variance; ATG: autophagy related; BSA: bovine serum albumin; cDNA: complementary deoxyribonucleic acid; CEP: cartilaginous endplates; CHX: cycloheximide; cKO: conditional knockout; Cor: coronal plane; CT: computed tomography; Cy: coccygeal vertebra; D: aspartic acid; DEG: differentially expressed gene; DHI: disc height index; DIBA: dot immunobinding assay; dUTP: 2'-deoxyuridine 5'-triphosphate; ECM: extracellular matrix; EDTA: ethylene diamine tetraacetic acid; ER: endoplasmic reticulum; FBS: fetal bovine serum; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GPS: group-based prediction system; GSEA: gene set enrichment analysis; GTP: guanosine triphosphate; HE: hematoxylin-eosin; HRP: horseradish peroxidase; IDD: intervertebral disc degeneration; IF: immunofluorescence staining; IL1: interleukin 1; IVD: intervertebral disc; KEGG: Kyoto encyclopedia of genes and genomes; KRT8: keratin 8; KD: knockdown; KO: knockout; L: lumbar vertebra; LBP: low back pain; LC/MS: liquid chromatograph mass spectrometer; LSI: mouse lumbar instability model; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MMP3: matrix metallopeptidase 3; MRI: nuclear magnetic resonance imaging; NC: negative control; NP: nucleus pulposus; PBS: phosphate-buffered saline; PE: p-phycoerythrin; PFA: paraformaldehyde; PI: propidium iodide; PKN: protein kinase N; OE: overexpression; PTM: post translational modification; PVDF: polyvinylidene fluoride; qPCR: quantitative reverse-transcriptase polymerase chain reaction; RHOA: ras homolog family member A; RIPA: radio immunoprecipitation assay; RNA: ribonucleic acid; ROS: reactive oxygen species; RT: room temperature; TCM: rat tail compression-induced IDD model; TCS: mouse tail suturing compressive model; S: serine; Sag: sagittal plane; SD rats: Sprague-Dawley rats; shRNA: short hairpin RNA; siRNA: small interfering RNA; SOFG: safranin O-fast green; SQSTM1: sequestosome 1; TUNEL: terminal deoxynucleotidyl transferase dUTP nick end labeling; VG/ml: viral genomes per milliliter; WCL: whole cell lysate.

PHLPP1 deficiency protects against age-related intervertebral disc degeneration

Background

Intervertebral disc (IVD) degeneration is strongly associated with low back pain and is highly prevalent in the elderly population. Hallmarks of IVD degeneration include cell loss and extracellular matrix degradation. The PH domain leucine-rich-repeats protein phosphatase (PHLPP1) is highly expressed in diseased cartilaginous tissues where it is linked to extracellular matrix degradation. This study explored the ability of PHLPP1 deficiency to protect against age-related spontaneous IVD degeneration.

Methods

Lumbar IVDs of global Phlpp1 knockout (KO) and wildtype (WT) mice were collected at 5 months (young) and 20 months (aged). Picrosirius red-alcian blue staining (PR-AB) was performed to examine IVD structure and histological score. The expression of aggrecan, ADAMTS5, KRT19, FOXO1 and FOXO3 was analyzed through immunohistochemistry. Cell apoptosis was assessed by TUNEL assay. Human nucleus pulposus (NP) samples were obtained from patients diagnosed with IVD degeneration. PHLPP1 knockdown in human degenerated NP cells was conducted using small interfering RNA (siRNA) transfection. The expression of PHLPP1 regulated downstream targets was analyzed via immunoblot and real time quantitative PCR.

Results

Histological analysis showed that Phlpp1 KO decreased the prevalence and severity of age-related IVD degeneration. The deficiency of PHLPP1 promoted the increased expression of NP phenotypic marker KRT19, aggrecan and FOXO1, and decreased levels of ADMATS5 and cell apoptosis in the NP of aged mice. In degenerated human NP cells, PHLPP1 knockdown induced FOXO1 protein levels while FOXO1 inhibition offset the beneficial effects of PHLPP1 knockdown on KRT19 gene and protein expression.

Conclusions

Our findings indicate that Phlpp1 deficiency protected against NP phenotypic changes, extracellular matrix degradation, and cell apoptosis in the process of IVD degeneration, probably through FOXO1 activation, making PHLPP1 a promising therapeutic target for treating IVD degeneration.

Optineurin-mediated mitophagy as a potential therapeutic target for intervertebral disc degeneration

Low back pain is thought to be mainly caused by intervertebral disc degeneration (IVDD), and there is a lack of effective treatments. Cellular senescence and matrix degradation are important factors that cause disc degeneration. Mitochondrial dysfunction induced by oxidative stress is an important mechanism of cellular senescence and matrix degradation in the nucleus pulposus (NP), and mitophagy can effectively remove damaged mitochondria, restore mitochondrial homeostasis, and mitigate the damage caused by oxidative stress. Optineurin (OPTN) is a selective mitophagy receptor, and its role in intervertebral disc degeneration remains unclear. Here, we aimed to explore the effect of OPTN on H₂O₂-induced nucleus pulposus cell (NPCs) senescence and matrix degradation in a rat model of disc degeneration. Western blot analysis showed that OPTN expression was reduced in degenerative human and rat nucleus pulposus tissues and increased in H₂O₂-induced senescent NPCs. OPTN overexpression significantly inhibited H₂O₂-induced senescence and increased matrix-associated protein expression in NPCs, but OPTN knockdown showed the opposite effect. As previous reports have suggested that mitophagy significantly reduces mitochondrial damage and reactive oxygen species (ROS) caused by oxidative stress, and we used the mitophagy agonist CCCP, the mitophagy inhibitor cyclosporin A (CsA), and the mitochondrial ROS (mtROS) scavenger mitoTEMPO and confirmed that OPTN attenuated NPCs senescence and matrix degeneration caused by oxidative stress by promoting mitophagy to scavenge damaged mitochondria and excess reactive oxygen species, thereby slowing the progression of IVDD. In conclusion, our research suggests that OPTN is involved in IVDD and exerts beneficial effects against IVDD.

Raloxifene Stimulates Estrogen Signaling to Protect Against Age- and Sex-Related Intervertebral Disc Degeneration in Mice

Estrogen agonist raloxifene is an FDA-approved treatment of osteoporosis in postmenopausal women, which may also be a promising prophylactic for painful intervertebral disc (IVD) degeneration. Here, we hypothesized that 1) aging and biological sex contribute to IVD degeneration by reducing estrogen signaling and that 2) raloxifene stimulates estrogen signaling to protect against age- and sex-related IVD degeneration in mice. 2.5-month-old (male and female) and 22.5-month-old (female) C57Bl/6J mice were subcutaneously injected with raloxifene hydrochloride 5x/week for 6 weeks (n = 7-9/grp). Next, female mice were ovariectomized (OVX) or sham operated at 4 months of age and tissues harvested at 6 months (n = 5-6/grp). Advanced aging and OVX increased IVD degeneration score, weakened IVD strength, reduced estrogen receptor-α (ER-α) protein expression, and increased neurotransmitter substance P (SP) expression. Similar to aging and compared with male IVDs, female IVDs were more degenerated, mechanically less viscoelastic, and expressed less ER-α protein, but unlike the effect induced by aging or OVX, IVD mechanical force was greater in females than in males. Therapeutically, systemic injection of raloxifene promoted ER-α protein to quell these dysregulations by enlarging IVD height, alleviating IVD degeneration score, increasing the strength and viscoelastic properties of the IVD, and reducing IVD cell expression of SP in young-adult and old female mice. Transcriptionally, injection of raloxifene upregulated the gene expression of ER-α and extracellular matrix-related anabolism in young-adult and old IVD. In vertebra, advanced aging and OVX reduced trabecular BV/TV, whereas injection of raloxifene increased trabecular BV/TV in young-adult and old female mice, but not in young-adult male mice. In vertebra, advanced aging, OVX, and biological sex (females > males) increased the number of SP-expressing osteocytes, whereas injection of raloxifene reduced the number of SP-expressing osteocytes in young-adult female and male mice and old female mice. Overall, injection of estrogen agonist raloxifene in mice normalized dysregulation of IVD structure, IVD mechanics, and pain-related SP expression in IVD cells and osteocytes induced by aging and biological sex. These data suggest that, in addition to bone loss, raloxifene may relieve painful IVD degeneration in postmenopausal women induced by advanced age, biological sex, and estrogen depletion.

High fat diet causes inferior vertebral structure and function without disc degeneration in RAGE-KO mice

Back pain and spinal pathologies are associated with obesity in juveniles and adults, yet studies identifying causal relationships are lacking and none investigate sex differences. This study determined if high fat (HF) diet causes structural and functional changes to vertebrae and intervertebral discs (IVDs); if these changes are modulated in mice with systematic ablation for the receptor for advanced glycation endproducts (RAGE-KO); and if these changes are sex-dependent. Wild-type (WT) and RAGE-KO mice were fed a low fat (LF) or HF diet for 12 weeks starting at 6 weeks, representing the juvenile population. HF diet led to weight/fat gain, glucose intolerance, and increased cytokine levels (IL-5, MIG, and RANTES); with less fat gain in RAGE-KO females. Most importantly, HF diet reduced vertebral trabecular bone volume fraction and compressive and shear moduli, without a modifying effect of RAGE-KO, but with a more pronounced effect in females. HF diet caused reduced cortical area fraction only in WT males. Neither HF diet nor RAGE-KO affected IVD degeneration grade. Biomechanical properties of coccygeal motion segments were affected by RAGE-KO but not diet, with some interactions identified. In conclusion, HF diet resulted in inferior vertebral structure and function with some sex differences, no IVD degeneration, and few modifying effects of RAGE-KO. These structural and functional deficiencies with HF diet provide further evidence that diet can affect spinal structures and may increase the risk for spinal injury and degeneration with aging and additional stressors. Back pain and spinal pathologies are associated with obesity in juveniles and adults, yet studies identifying causal relationships are lacking and none investigate sex differences.

In vivo Mouse Intervertebral Disc Degeneration Models and Their Utility as Translational Models of Clinical Discogenic Back Pain: A Comparative Review

Low back pain is a leading cause of disability worldwide and studies have demonstrated intervertebral disc (IVD) degeneration as a major risk factor. While many in vitro models have been developed and used to study IVD pathophysiology and therapeutic strategies, the etiology of IVD degeneration is a complex multifactorial process involving crosstalk of nearby tissues and systemic effects. Thus, the use of appropriate in vivo models is necessary to fully understand the associated molecular, structural, and functional changes and how they relate to pain. Mouse models have been widely adopted due to accessibility and ease of genetic manipulation compared to other animal models. Despite their small size, mice lumbar discs demonstrate significant similarities to the human IVD in terms of geometry, structure, and mechanical properties. While several different mouse models of IVD degeneration exist, greater standardization of the methods for inducing degeneration and the development of a consistent set of output measurements could allow mouse models to become a stronger tool for clinical translation. This article reviews current mouse models of IVD degeneration in the context of clinical translation and highlights a critical set of output measurements for studying disease pathology or screening regenerative therapies with an emphasis on pain phenotyping. First, we summarized and categorized these models into genetic, age-related, and mechanically induced. Then, the outcome parameters assessed in these models are compared including, molecular, cellular, functional/structural, and pain assessments for both evoked and spontaneous pain. These comparisons highlight a set of potential key parameters that can be used to validate the model and inform its utility to screen potential therapies for IVD degeneration and their translation to the human condition. As treatment of symptomatic pain is important, this review provides an emphasis on critical pain-like behavior assessments in mice and explores current behavioral assessments relevant to discogenic back pain. Overall, the specific research question was determined to be essential to identify the relevant model with histological staining, imaging, extracellular matrix composition, mechanics, and pain as critical parameters for assessing degeneration and regenerative strategies.

Expansion of FGFR3-positive nucleus pulposus cells plays important roles in postnatal nucleus pulposus growth and regeneration

BACKGROUND

Intervertebral disc degeneration (IVDD) can cause low back pain, a major public health concern. IVDD is characterized with loss of cells especially those in nucleus pulposus (NP), due to the limited proliferative potential and regenerative ability. Few studies, however, have been carried out to investigate the in vivo proliferation events of NP cells and the cellular contribution of a specific subpopulation of NP during postnatal growth or regeneration.

METHODS

We generated FGFR3-3*Flag-IRES-GFP mice and crossed FGFR3-CreERT2 mice with Rosa26-mTmG, Rosa26-DTA and Rosa26-Confetti mice, respectively, to perform inducible genetic tracing studies.

RESULTS

Expression of FGFR3 was found in the outer region of NP with co-localized expressions of proliferating markers. By fate mapping studies, FGFR3-positive (FGFR3⁺) NP cells were found proliferate from outer region to inner region of NP during postnatal growth. Clonal lineage tracing by Confetti mice and ablation of FGFR3^·+ NP cells by DTA mice further revealed that the expansion of the FGFR3⁺ cells was required for the morphogenesis and homeostasis of postnatal NP. Moreover, in degeneration and regeneration model of mouse intervertebral disc, FGFR3⁺ NP cells underwent extensive expansion during the recovery stage.

CONCLUSION

Our present work demonstrates that FGFR3⁺ NP cells are novel subpopulation of postnatal NP with long-existing proliferative capacity shaping the adult NP structure and participating in the homeostasis maintenance and intrinsic repair of NP. These findings may facilitate the development of new therapeutic approaches for IVD regeneration.

Suppression of Sost/Sclerostin and Dickkopf-1 Augment Intervertebral Disc Structure in Mice

Intervertebral disc (IVD) degeneration is a leading cause of low back pain, characterized by accelerated extracellular matrix breakdown and IVD height loss, but there is no approved pharmacological therapeutic. Deletion of Wnt ligand competitor Lrp5 induces IVD degeneration, suggesting that Wnt signaling is essential for IVD homeostasis. Therefore, the IVD may respond to neutralization of Wnt ligand competitors sost(gene)/sclerostin(protein) and/or dickkopf-1 (dkk1). Anti-sclerostin antibody (scl-Ab) is an FDA-approved bone therapeutic that activates Wnt signaling. We aimed to (i) determine if pharmacological neutralization of sclerostin, dkk1, or their combination would stimulate Wnt signaling and augment IVD structure and (ii) determine the prolonged adaptation of the IVD to global, persistent deletion of sost. Nine-week-old C57Bl/6J female mice (n = 6-7/group) were subcutaneously injected 2×/week for 5.5 weeks with scl-Ab (25 mg/kg), dkk1-Ab (25 mg/kg), 3:1 scl-Ab/dkk1-Ab (18.75:6.25 mg/kg), or vehicle (veh). Separately, IVD of sost KO and wild-type (WT) mice (n = 8/group) were harvested at 16 weeks of age. First, compared with vehicle, injection of scl-Ab, dkk1-Ab, and 3:1 scl-Ab/dkk1-Ab similarly increased lumbar IVD height and β-catenin gene expression. Despite these similarities, only injection of scl-Ab alone strengthened IVD mechanical properties and decreased heat shock protein gene expressions. Genetically and compared with WT, sost KO enlarged IVD height, increased proteoglycan staining, and imbibed IVD hydration. Notably, persistent deletion of sost was compensated by upregulation of dkk1, which consequently reduced the cell nuclear fraction for Wnt signaling co-transcription factor β-catenin in the IVD. Lastly, RNA-sequencing pathway analysis confirmed the compensatory suppression of Wnt signaling and revealed a reduction of cellular stress-related pathways. Together, suppression of sost/sclerostin or dkk1 each augmented IVD structure by stimulating Wnt signaling, but scl-Ab outperformed dkk1-Ab in strengthening the IVD. Ultimately, postmenopausal women prescribed scl-Ab injections to prevent vertebral fracture may also benefit from a restoration of IVD height and health. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Platelet-Derived Growth Factor-BB Inhibits Intervertebral Disc Degeneration via Suppressing Pyroptosis and Activating the MAPK Signaling Pathway

Platelet-derived growth factor-BB (PDGF-BB) is a cytokine involved in tissue repair and tumor progression. It has been found to have expression differences between normal and degenerative intervertebral discs. However, it is not clear whether PDGF-BB has a protective effect on intervertebral disc degeneration (IDD). In this experiment, we treated nucleus pulposus cells (NPCs) with IL-1β to simulate an inflammatory environment and found that the extracellular matrix (ECM) anabolic function of NPCs in an inflammatory state was inhibited. Moreover, the induction of IL-1β also enhanced the expression of NLRP3 and the cleavage of caspase-1 and IL-1β, which activated the pyroptosis of NPCs. In this study, we studied the effect of PDGF-BB on IL-1β-treated NPCs and found that PDGF-BB not only significantly promotes the ECM anabolism of NPCs, but also inhibits the occurrence of pyroptosis and the production of pyroptosis products of NPCs. Consistent with this, when we used imatinib to block the PDGF-BB receptor, the above-mentioned protective effect disappeared. In addition, we found that PDGF-BB can also promote the ECM anabolism of NPCs by regulating the ERK, JNK, PI3K/AKT signaling pathways, but not the P38 signaling pathway. In vivo studies, mice that blocked PDGF-BB receptors showed more severe histological manifestations of intervertebral disc degeneration. In summary, our results indicate that PDGF-BB participates in inhibiting the occurrence and development of IDD by inhibiting pyroptosis and regulating the MAPK signaling pathway.

Kindlin-2 inhibits Nlrp3 inflammasome activation in nucleus pulposus to maintain homeostasis of the intervertebral disc

Intervertebral disc (IVD) degeneration (IVDD) is the main cause of low back pain with major social and economic burdens; however, its underlying molecular mechanisms remain poorly defined. Here we show that the focal adhesion protein Kindlin-2 is highly expressed in the nucleus pulposus (NP), but not in the anulus fibrosus and the cartilaginous endplates, in the IVD tissues. Expression of Kindlin-2 is drastically decreased in NP cells in aged mice and severe IVDD patients. Inducible deletion of Kindlin-2 in NP cells in adult mice causes spontaneous and striking IVDD-like phenotypes in lumbar IVDs and largely accelerates progression of coccygeal IVDD in the presence of abnormal mechanical stress. Kindlin-2 loss activates Nlrp3 inflammasome and stimulates expression of IL-1β in NP cells, which in turn downregulates Kindlin-2. This vicious cycle promotes extracellular matrix (ECM) catabolism and NP cell apoptosis. Furthermore, abnormal mechanical stress reduces expression of Kindlin-2, which exacerbates Nlrp3 inflammasome activation, cell apoptosis, and ECM catabolism in NP cells caused by Kindlin-2 deficiency. In vivo blocking Nlrp3 inflammasome activation prevents IVDD progression induced by Kindlin-2 loss and abnormal mechanical stress. Of translational significance, adeno-associated virus-mediated overexpression of Kindlin-2 inhibits ECM catabolism and cell apoptosis in primary human NP cells in vitro and alleviates coccygeal IVDD progression caused by mechanical stress in rat. Collectively, we establish critical roles of Kindlin-2 in inhibiting Nlrp3 inflammasome activation and maintaining integrity of the IVD homeostasis and define a novel target for the prevention and treatment of IVDD.

Local Delivery of Senolytic Drug Inhibits Intervertebral Disc Degeneration and Restores Intervertebral Disc Structure

Intervertebral disc (IVD) degeneration (IVDD) is a leading cause of chronic low back pain. There is a strong clinical demand for more effective treatments for IVDD as conventional treatments provide only symptomatic relief rather than arresting IVDD progression. This study shows that senolytic therapy with local drug delivery can inhibit IVDD and restore IVD integrity. ABT263, a senolytic drug, is loaded in poly(lactic-co-glycolic acid) nanoparticles (PLGA-ABT) and intradiscally administered into injury-induced IVDD rat models. The single intradiscal injection of PLGA-ABT may enable local delivery of the drug to avascular IVD, prevention of potential systemic toxicity caused by systemic administration of senolytic drug, and morbidity caused by repetitive injections of free drug into the IVD. The strategy results in the selective elimination of senescent cells from the degenerative IVD, reduces expressions of pro-inflammatory cytokines and matrix proteases in the IVD, inhibits progression of IVDD, and even restores the IVD structure. This study demonstrates for the first time that local delivery of senolytic drug can effectively treat senescence-associated IVDD. This approach can be extended to treat other types of senescence-associated degenerative diseases.

Epigenetic modification of miR-217 promotes intervertebral disc degeneration by targeting the FBXO21-ERK signalling pathway

BACKGROUND

Numerous potential therapeutic alternatives for intervertebral disc degeneration (IDD) have been investigated, the most promising of which are based on biological variables such as microRNAs (miRNAs). Therefore, we verified the hypothesis that miRNAs modulate IDD by affecting the FBXO21-ERK signalling pathway.

METHODS

Microarray and quantitative real-time polymerase chain reaction (RT-qPCR) tests were used to examine the expression profiles of miRNAs in nucleus pulposus (NP) cells between patients with IDD and controls. Western blotting and luciferase reporter assays were used to identify the miRNA targets.

RESULTS

Microarray and RT-qPCR assays confirmed that the expression level of miR-217 was significantly decreased in degenerative NP cells. CpG islands were predicted in the miR-217 promoter region. The IDD group had considerably higher methylation than the control group. Gain- and loss-of-function experiments revealed that miR-217 mimics inhibited apoptosis and extracellular matrix (ECM) breakdown in NP cells. Bioinformatic analyses and luciferase assays were used to determine the connection between miR-217 and FBXO21. In vitro tests revealed that miR-217 mimics inhibited the expression of FBXO21, pERK, MMP13, and ADAMTS5 proteins, successfully protecting the ECM from degradation. Additionally, in vivo investigation using the IDD mouse model demonstrated that the miR-217 agonist may sufficiently promote NP cell proliferation, decrease apoptosis, promote ECM synthesis, and suppress the expression of matrix-degrading enzymes in NP cells.

CONCLUSIONS

Overexpression of miR-217 inhibits IDD via FBXO21/ERK regulation.

TRIAL REGISTRATION

This study was performed in strict accordance with the NIH guidelines for the care and use of laboratory animals (NIH Publication No. 85-23 Rev. 1985) and was approved by the human research ethics committee of Wuhan University Renmin Hospital (Approval No. RMHREC-D-2020-391), and written informed consent was obtained from each participant.

Tenomodulin and Chondromodulin-1 Are Both Required to Maintain Biomechanical Function and Prevent Intervertebral Disc Degeneration

OBJECTIVE

The underlying mechanisms and molecular factors influencing intervertebral disc (IVD) homeostasis and degeneration remain clinically relevant. Tenomodulin (Tnmd) and chondromodulin (Chm1) are antiangiogenic transmembrane glycoproteins, with cleavable C-terminus, expressed by IVD cells that are implicated in the onset of degenerative processes. We evaluate the organ-level biomechanical impact of knocking out Tnmd alone, and Tnmd and Chm1, simultaneously.

DESIGN

Caudal (c5-8) and lumbar vertebrae (L1-4) of skeletally mature male and female 9-month-old wildtype (WT), Tnmd knockout (Tnmd^-/-), and Tnmd/Chm1 double knockout (Tnmd^-/-/Chm^-/-) mice were used (n = 9-13 per group). Disc height index (DHI), histomorphological changes, and axial, torsional, creep, and failure biomechanical properties were evaluated. Differences were assessed by one-way ANOVA with post hoc Bonferroni-corrected comparisons (P < 0.05).

RESULTS

Tnmd^-/-/Chm1^-/- IVDs displayed increased DHI and histomorphological scores that indicated increased IVD degeneration compared to the WT and Tnmd^-/- groups. Double knockout IVDs required significantly less torque and energy to initiate torsional failure. Creep parameters were comparable between all groups, except for the slow time constant, which indicated faster outward fluid flow. Tnmd^-/- IVDs lost fluid faster than the WT group, and this effect was amplified in the double knockout IVDs.

CONCLUSION

Knocking out Tnmd and Chm1 affects IVD fluid flow and organ-level biomechanical function and therefore may play a role in contributing to IVD degeneration. Larger effects of the Tnmd and Chm1 double knockout mice compared to the Tnmd single mutant suggest that Chm1 may play a compensatory role in the Tnmd single mutant IVDs.

MicroRNA-338-3p as a novel therapeutic target for intervertebral disc degeneration

Recent studies have demonstrated the pivotal role played by microRNAs (miRNAs) in the etiopathogenesis of intervertebral disc degeneration (IDD). The study of miRNA intervention in IDD models may promote the advancement of miRNA-based therapeutic strategies. The aim of the current study was to investigate whether intradiscal delivery of miRNA can attenuate IDD development. Our results showed that miR-338-3p expression was significantly increased in the nucleus pulposus (NP) of patients with IDD. Moreover, there was a statistically significant positive correlation between the expression level of miR-338-3p and the severity of IDD. Our functional studies showed that miR-338-3p significantly influenced the expression of extracellular matrix synthesis genes, as well as the proliferation and apoptosis of NP cells. Mechanistically, miR-338-3p aggravated IDD progression by directly targeting SIRT6, a negative regulator of the MAPK/ERK pathway. Intradiscal injection of antagomir-338-3p significantly decelerated IDD development in mouse models. Our study is the first to identify miR-338-3p as a mediator of IDD and thus may be a promising target for rescuing IDD.

TRPV4 mediates cell damage induced by hyperphysiological compression and regulates COX2/PGE2 in intervertebral discs

BACKGROUND

Aberrant mechanical loading of the spine causes intervertebral disc (IVD) degeneration and low back pain. Current therapies do not target the mediators of the underlying mechanosensing and mechanotransduction pathways, as these are poorly understood. This study investigated the role of the mechanosensitive transient receptor potential vanilloid 4 (TRPV4) ion channel in dynamic compression of bovine nucleus pulposus (NP) cells in vitro and mouse IVDs in vivo.

METHODS

Degenerative changes and the expression of the inflammatory mediator cyclooxygenase 2 (COX2) were examined histologically in the IVDs of mouse tails that were dynamically compressed at a short repetitive hyperphysiological regime (vs sham). Bovine NP cells embedded in an agarose-collagen hydrogel were dynamically compressed at a hyperphysiological regime in the presence or absence of the selective TRPV4 antagonist GSK2193874. Lactate dehydrogenase (LDH) and prostaglandin E2 (PGE2) release, as well as phosphorylation of mitogen-activated protein kinases (MAPKs), were analyzed. Degenerative changes and COX2 expression were further evaluated in the IVDs of trpv4-deficient mice (vs wild-type; WT).

RESULTS

Dynamic compression caused IVD degeneration in vivo as previously shown but did not affect COX2 expression. Dynamic compression significantly augmented LDH and PGE2 releases in vitro, which were significantly reduced by TRPV4 inhibition. Moreover, TRPV4 inhibition during dynamic compression increased the activation of the extracellular signal-regulated kinases 1/2 (ERK) MAPK pathway by 3.13-fold compared to non-compressed samples. Trpv4-deficient mice displayed mild IVD degeneration and decreased COX2 expression compared to WT mice.

CONCLUSIONS

TRPV4 therefore regulates COX2/PGE2 and mediates cell damage induced by hyperphysiological dynamic compression, possibly via ERK. Targeted TRPV4 inhibition or knockdown might thus constitute promising therapeutic approaches to treat patients suffering from IVD pathologies caused by aberrant mechanical stress.

Histological differences between lumbar and tail intervertebral discs in mice

Both the lumbar and tail intervertebral discs (IVD) of mice serve as models for the pathogenesis and histologic progression of degenerative disc disease. Recent studies in mature mice, however, demonstrate that the mechanics and physical attributes of lumbar and tail IVD‐endplate (EP)‐interfaces are strikingly different. We hypothesized that these structural disparities are associated with differences in the composition and organization of soft tissue elements that influence the biomechanical properties of the spine. Lumbar and tail vertebral segments and discs were collected from the same C57BL/6N and C57BL/6JRj mice, respectively for histological comparison of coronal sections at the ages of 4 weeks (weaned, both strains, C57BL/6N: n = 7; C57BL/6JRj: n = 4), three (mature, C57BL/6N: n = 7; C57BL/6JRj: n = 4), twelve (middle aged, C57BL/6JRj only: n = 3) and eighteen (old, C57BL/6JRj only: n = 3) months old. The histology of lumbar and tail IVD‐EP‐interfaces of mature mice differed markedly. The lumbar IVD‐EP‐interphase was characterized by a broad cartilaginous EP, while the tail IVD‐EP‐interphase comprised a thin layer of cartilage cells adjacent to a broad bony layer abutting the vertebral growth plate. Furthermore, the composition of the nuclei pulposi (NP) of lumbar and tail IVD in mature mice differed greatly. Lumbar NP consisted of a compact cluster of mainly large, uni‐vacuolated cells centered in an amorphous matrix, while tail NP were composed of a loose aggregate of vacuolated and non‐vacuolated cells. The anuli fibrosi also differed, with more abundant and sharply defined lamellae in tail compared to lumbar discs. The observed histological differences in the EP were even most prominent in weaned mice but were still discernible in middle‐aged and old mice. An appreciation of the histological differences between lumbar and tail IVD components in mice, including nucleus pulposus, annulus fibrosus, and endplates, is essential to our understanding of spinal biomechanics in these animals and should inform the design and interpretation of future IVD‐studies.

Development of a standardized histopathology scoring system using machine learning algorithms for intervertebral disc degeneration in the mouse model-An ORS spine section initiative

Mice have been increasingly used as preclinical model to elucidate mechanisms and test therapeutics for treating intervertebral disc degeneration (IDD). Several intervertebral disc (IVD) histological scoring systems have been proposed, but none exists that reliably quantitate mouse disc pathologies. Here, we report a new robust quantitative mouse IVD histopathological scoring system developed by building consensus from the spine community analyses of previous scoring systems and features noted on different mouse models of IDD. The new scoring system analyzes 14 key histopathological features from nucleus pulposus (NP), annulus fibrosus (AF), endplate (EP), and AF/NP/EP interface regions. Each feature is categorized and scored; hence, the weight for quantifying the disc histopathology is equally distributed and not driven by only a few features. We tested the new histopathological scoring criteria using images of lumbar and coccygeal discs from different IDD models of both sexes, including genetic, needle-punctured, static compressive models, and natural aging mice spanning neonatal to old age stages. Moreover, disc sections from common histological preparation techniques and stains including H&E, SafraninO/Fast green, and FAST were analyzed to enable better cross-study comparisons. Fleiss's multi-rater agreement test shows significant agreement by both experienced and novice multiple raters for all 14 features on several mouse models and sections prepared using various histological techniques. The sensitivity and specificity of the new scoring system was validated using artificial intelligence and supervised and unsupervised machine learning algorithms, including artificial neural networks, k-means clustering, and principal component analysis. Finally, we applied the new scoring system on established disc degeneration models and demonstrated high sensitivity and specificity of histopathological scoring changes. Overall, the new histopathological scoring system offers the ability to quantify histological changes in mouse models of disc degeneration and regeneration with high sensitivity and specificity.

Deleterious effects of whole-body vibration on the spine: A review of in vivo, ex vivo, and in vitro models

Occupational exposure to whole-body vibration is associated with the development of musculoskeletal, neurological, and other ailments. Low back pain and other spine disorders are prevalent among those exposed to whole-body vibration in occupational and military settings. Although standards for limiting exposure to whole-body vibration have been in place for decades, there is a lack of understanding of whole-body vibration-associated risks among safety and healthcare professionals. Consequently, disorders associated with whole-body vibration exposure remain prevalent in the workforce and military. The relationship between whole-body vibration and low back pain in humans has been established largely through cohort studies, for which vibration inputs that lead to symptoms are rarely, if ever, quantified. This gap in knowledge highlights the need for the development of relevant in vivo, ex vivo, and in vitro models to study such pathologies. The parameters of vibrational stimuli (eg, frequency and direction) play critical roles in such pathologies, but the specific cause-and-effect relationships between whole-body vibration and spinal pathologies remain mostly unknown. This paper provides a summary of whole-body vibration parameters; reviews in vivo, ex vivo, and in vitro models for spinal pathologies resulting from whole-body vibration; and offers suggestions to address the gaps in translating injury biomechanics data to inform clinical practice.

Krüppel like factor 10 prevents intervertebral disc degeneration via TGF-β signaling pathway both in vitro and in vivo

Background

Krüppel like factor 10 (KLF10), which is also known as TGF-β Inducible Early Gene-1 (TIEG1), plays a crucial role in regulating cell proliferation, cell apoptosis and inflammatory reaction in human carcinoma cells. Moreover, KLF10 knockout in mice leads to severe defects associated with muscle, skeleton and heart etc. However, the function of KLF10 in intervertebral disc degeneration (IVDD) has not been reported yet.

Methods

The relationship between KLF10 and IVDD were investigated in nucleus pulposus (NP) tissues from human and rats. The role of KLF10 in NP cells was explored via loss or gain of function experiments. IVDD rat models were constructed through needle puncture and the effects of KLF10 in IVDD model of rats were investigated via intradiscal injection of KLF10.

Results

We first found that KLF10 was lowly expressed in degenerative NP tissues and the level of KLF10 showed negative correlation with the disc grades of IVDD patients. Loss or gain of function experiments demonstrated that KLF10 could inhibit apoptosis and enhance migration and proliferation of IL-1β induced NP cells. And KLF10 overexpression reduced extracellular matrix (ECM) degeneration and enhanced ECM synthesis, whereas knockdown of KLF10 resulted in adverse effects. These positive effects of KLF10 could be reversed by the inhibition of TGF-β signaling pathway. In vivo, KLF10 overexpression alleviated IVDD.

Conclusions

This is the first study to reveal that KLF10 was dysregulated in IVDD and overexpressed KLF10 could alleviate IVDD by regulating TGF-β signaling pathway both in vitro and in vivo, which were involved in prohibiting apoptosis, promoting proliferation and migration of NP cells.The translational potential of this article: Overexpression of KLF10 might be an effective therapeutic strategy in the treatment of IVDD.

Myocardin‑related transcription factor A nuclear translocation contributes to mechanical overload‑induced nucleus pulposus fibrosis in rats with intervertebral disc degeneration

Previous studies have reported that the Ras homolog family member A (RhoA)/myocardin‑related transcription factor A (MRTF‑A) nuclear translocation axis positively regulates fibrogenesis induced by mechanical forces in various organ systems. The aim of the present study was to determine whether this signaling pathway was involved in the pathogenesis of nucleus pulposus (NP) fibrosis induced by mechanical overload during the progression of intervertebral disc degeneration (IVDD) and to confirm the alleviating effect of an MRTF‑A inhibitor in the treatment of IVDD. NP cells (NPCs) were cultured on substrates of different stiffness (2.9 and 41.7 KPa), which mimicked normal and overloaded microenvironments, and were treated with an inhibitor of MRTF‑A nuclear import, CCG‑1423. In addition, bipedal rats were established by clipping the forelimbs of rats at 1 month and gradually elevating the feeding trough, and in order to establish a long‑term overload‑induced model of IVDD, and their intervertebral discs were injected with CCG‑1423 in situ. Cell viability was determined by Cell Counting Kit‑8 assay, and protein expression was determined by western blotting, immunofluorescence and immunohistochemical staining. The results demonstrated that the viability of NPCs was not affected by the application of force or the inhibitor. In NPCs cultured on stiff matrices, MRTF‑A was mostly localized in the nucleus, and the expression levels of fibrotic proteins, including type I collagen, connective tissue growth factor and α‑smooth muscle cell actin, were upregulated compared with those in NPCs cultured on soft matrices. The levels of these proteins were reduced by CCG‑1423 treatment. In rats, 6 months of upright posture activated MRTF‑A nuclear‑cytoplasmic trafficking and fibrogenesis in the NP and induced IVDD; these effects were alleviated by CCG‑1423 treatment. In conclusion, the results of the present study demonstrated that the RhoA/MRTF‑A translocation pathway may promote mechanical overload‑induced fibrogenic activity in NP tissue and partially elucidated the molecular mechanisms underlying the occurrence of IVDD.

The Role of miR-31-5p in the Development of Intervertebral Disc Degeneration and Its Therapeutic Potential

Intervertebral disc degeneration (IDD) refers to the abnormal response of cell-mediated progressive structural failure. In order to understand the molecular mechanism of the maintenance and destruction of the intervertebral disc, new IDD treatment methods are developed. Here, we first analyzed the key regulators of IDD through microRNAs microarrays. Then, the level of miR-31-5p was evaluated by qRT-PCR. The association between miR-31-5p and Stromal cell-derived factor 1 (SDF-1)/CXCR7 axis was assessed by 3′-untranslated region (UTR) cloning and luciferase assay. The apoptosis of cells under different treatments was evaluated by flow cytometer. The cell proliferation was assessed by EdU assay. After IDD model establishment, the discs of mice tail were harvested for histological and radiographic evaluation in each group. Finally, the protein levels of SDF-1, CXCR7, ADAMTS-5, Col II, Aggrecan, and MMP13 were assessed by western blot. The results show that miR-31-5p is a key regulator of IDD and its level is down-regulated in IDD. Overexpression of miR-31-5p facilitates nucleus pulposus cell proliferation, inhibits apoptosis, facilitates ECM formation, and inhibits the level of matrix degrading enzymes in NP cells. The SDF-1/CXCR7 axis is the direct target of miR-31-5p. miR-31-5p acts on IDD by regulating SDF-1/CXCR7. In vitro experiments further verified that the up-regulation of miR-31-5p prevented the development of IDD. In conclusion, overexpression of miR-31-5p can inhibit IDD by regulating SDF-1/CXCR7.

The Role of Panx3 in Age-Associated and Injury-Induced Intervertebral Disc Degeneration

Pannexin 3 (Panx3) is a mechanosensitive, channel-forming glycoprotein implicated in the progression of post-traumatic osteoarthritis. Despite evidence for Panx3 expression in the intervertebral disc (IVD), its function in this cartilaginous joint structure remained unknown. Using Panx3 knockout mice, this study investigated the role of Panx3 in age-associated IVD degeneration and degeneration induced by annulus fibrosus (AF) needle puncture. Loss of Panx3 did not significantly impact the progression of age-associated histopathological IVD degeneration; however, loss of Panx3 was associated with decreased gene expression of Acan, Col1a1, Mmp13 and Runx2 and altered localization of COLX in the IVD at 19 months-of-age. Following IVD injury in the caudal spine, histological analysis of wild-type mice revealed clusters of hypertrophic cells in the AF associated with increased pericellular proteoglycan accumulation, disruptions in lamellar organization and increased lamellar thickness. In Panx3 knockout mice, hypertrophic AF cells were rarely detected and AF structure was largely preserved post-injury. Interestingly, uninjured IVDs adjacent to the site of injury more frequently showed evidence of early nucleus pulposus degeneration in Panx3 knockout mice but remained healthy in wild-type mice. These findings suggest a role for Panx3 in mediating the adaptive cellular responses to altered mechanical stress in the IVD, which may buffer aberrant loads transferred to adjacent motion segments.

CircGLCE alleviates intervertebral disc degeneration by regulating apoptosis and matrix degradation through the targeting of miR-587/STAP1

The purpose of this study was to identify a specific circular RNA and to investigate its regulatory mechanism in intervertebral disc degeneration (IDD). CircGLCE was selected after microarray analyses and was further analysed by RT-qPCR and FISH. CircGLCE was found to stably exist in the cytoplasm of nucleus pulposus (NP) cells. It was downregulated in IDD. After silencing CircGLCE, its function was assessed with RT-qPCR, immunofluorescence analysis and flow cytometry. Knockdown of CircGLCE promoted apoptosis and induced the expression of matrix-degrading enzymes in NP cells. CircGLCE served as a miR-587 sponge in NP cells. Inhibiting miR-587 counteracted the IDD-enhancing effect caused by silencing CircGLCE. STAP1 served as the miRNA target that mediated the functions of miR-587. In an IDD mouse model, the in vivo effects of overexpressing CircGLCE on IDD were confirmed by imaging techniques, TUNEL staining, FISH, western blotting, H&E staining and immunohistochemistry. Thus, CircGLCE attenuates IDD by inhibiting the apoptosis of NP cells and ECM degradation through the targeting of miR-587/STAP1. CircGLCE may be a potential therapeutic target for IDD treatments.

An Injectable Hyaluronan-Methylcellulose (HAMC) Hydrogel Combined with Wharton's Jelly-Derived Mesenchymal Stromal Cells (WJ-MSCs) Promotes Degenerative Disc Repair

Intervertebral disc (IVD) degeneration is one of the predominant causes of chronic low back pain (LBP), which is a leading cause of disability worldwide. Despite substantial progress in cell therapy for the treatment of IVD degeneration, significant challenges remain for clinical application. Here, we investigated the effectiveness of hyaluronan-methylcellulose (HAMC) hydrogels loaded with Wharton's Jelly-derived mesenchymal stromal cell (WJ-MSCs) in vitro and in a rat coccygeal IVD degeneration model. Following induction of injury-induced IVD degeneration, female Sprague-Dawley rats were randomized into four groups to undergo a single intradiscal injection of the following: (1) phosphate buffered saline (PBS) vehicle, (2) HAMC, (3) WJ-MSCs (2 × 10⁴ cells), and (4) WJ-MSCs-loaded HAMC (WJ-MSCs/HAMC) (n = 10/each group). Coccygeal discs were removed following sacrifice 6 weeks after implantation for radiologic and histologic analysis. We confirmed previous findings that encapsulation in HAMC increases the viability of WJ-MSCs for disc repair. The HAMC gel maintained significant cell viability in vitro. In addition, combined implantation of WJ-MSCs and HAMC significantly promoted degenerative disc repair compared to WJ-MSCs alone, presumably by improving nucleus pulposus cells viability and decreasing extracellular matrix degradation. Our results suggest that WJ-MSCs-loaded HAMC promotes IVD repair more effectively than cell injection alone and supports the potential clinical use of HAMC for cell delivery to arrest IVD degeneration or to promote IVD regeneration.