Caspase 3 as a therapeutic target for regulation of intervertebral disc degeneration in rabbits

Bone Marrow Aspirate Concentrate Combined with Ultra-Purified Alginate Bioresorbable Gel Enhances Intervertebral Disc Repair in a Canine Model: A Preclinical Proof-of-Concept Study

Although discectomy is commonly performed for lumbar intervertebral disc (IVD) herniation, the capacity for tissue repair after surgery is limited, resulting in residual lower back pain, recurrence of IVD herniation, and progression of IVD degeneration. Cell-based therapies, as one-step procedures, are desirable for enhancing IVD repair. This study aimed to investigate the therapeutic efficacy of a combination of newly developed ultra-purified alginate (UPAL) gel and bone marrow aspirate concentrate (BMAC) implantation for IVD repair after discectomy. Prior to an in vivo study, the cell concentration abilities of three commercially available preparation kits for creating the BMAC were compared by measuring the number of bone marrow mesenchymal stem cells harvested from the bone marrow of rabbits. Subsequently, canine-derived BMAC was tested in a canine model using a kit which had the highest concentration rate. At 24 weeks after implantation, we evaluated the changes in the magnetic resonance imaging (MRI) signals as well as histological degeneration grade and immunohistochemical analysis results for type II and type I collagen-positive cells in the treated IVDs. In all quantitative evaluations, such as MRI and histological and immunohistochemical analyses of IVD degeneration, BMAC-UPAL implantation significantly suppressed the progression of IVD degeneration compared to discectomy and UPAL alone. This preclinical proof-of-concept study demonstrated the potential efficacy of BMAC-UPAL gel as a therapeutic strategy for implementation after discectomy, which was superior to UPAL and discectomy alone in terms of tissue repair and regenerative potential.

Apoptosis activation during Lagovirus europaeus/GI.2 infection in rabbits

Rabbit Haemorrhagic Disease (RHD) is a severe disease caused by Lagovirus europaeus/GI.1 and GI.2. Immunological processes such as apoptosis are important factors involved in the pathogenesis of Rabbit Haemorrhagic Disease (RHD). The process of programmed cell death has been quite well characterized in infection with GI.1 strains, but apoptosis in infection with GI.2 strains has not been widely studied. This is particularly important as several studies have shown that significant differences in the host immune response are observed during infection with different strains of Lagovirus europaeus. In this study, we analyzed the gene expression, protein levels and activity of key apoptotic cell death factors in the spleen, kidney, lung, and heart of rabbits. As a result, we showed that there is a significant increase in caspase-3, Bax, Bcl2 and Bax/Bcl2 mRNA gene expression ratio in organs of infected animals. Our results show also increased levels of cleaved caspase-3, caspase-6 and PARP. Moreover, significant activity of caspase-3 was also detected. Our results indicate that caspase-3, caspase-6 and genes coding Bcl2 family proteins play a key role in the apoptotic response in Lagovirus europaeus/GI.2 infection in organs that are not the target of virus replication.

Apoptotic Cell Death in an Animal Model of Virus-Induced Acute Liver Failure-Observations during Lagovirus europaeus/GI.2 Infection

Lagovirus europaeus/GI.2 causes severe and highly fatal Rabbit Hemorrhagic Disease (RHD). Because of its characteristics, this infection is used as an animal model for acute liver failure (ALF). Apoptosis is one of the key processes underlying ALF and has been described as one of the mechanisms of RHD pathogenesis. Apoptotic cell death has been quite well characterized in infection with different variants of GI.1 strains, but so far, the GI.2 genotype has not been widely studied. In this study, we performed an evaluation of apoptotic cell death in hepatocytes of rabbits infected with Lagovirus europaeus/GI.2. We analyzed the expression of genes involved in apoptotic cell death by real-time PCR and performed immunohistochemical (IHC) assays. We showed a significant increase in the expression of caspase-3 and the proapoptotic Bax and anti-apoptotic Bcl-2 in infected animals. In addition, we recorded increased Bax/Bcl-2 ratios. IHC analyses showed the presence of morphological signs of apoptosis in the hepatocytes of infected rabbits. Our results indicate that caspase-3 and proteins from the Bcl-2 families play a key role in apoptosis induced by Lagovirus europaeus/GI.2 infection.

A Review: Methodologies to Promote the Differentiation of Mesenchymal Stem Cells for the Regeneration of Intervertebral Disc Cells Following Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration (IDD), a highly prevalent pathological condition worldwide, is widely associated with back pain. Treatments available compensate for the impaired function of the degenerated IVD but typically have incomplete resolutions because of their adverse complications. Therefore, fundamental regenerative treatments need exploration. Mesenchymal stem cell (MSC) therapy has been recognized as a mainstream research objective by the World Health Organization and was consequently studied by various research groups. Implanted MSCs exert anti-inflammatory, anti-apoptotic, and anti-pyroptotic effects and promote extracellular component production, as well as differentiation into IVD cells themselves. Hence, the ultimate goal of MSC therapy is to recover IVD cells and consequently regenerate the extracellular matrix of degenerated IVDs. Notably, in addition to MSC implantation, healthy nucleus pulposus (NP) cells (NPCs) have been implanted to regenerate NP, which is currently undergoing clinical trials. NPC-derived exosomes have been investigated for their ability to differentiate MSCs from NPC-like phenotypes. A stable and economical source of IVD cells may include allogeneic MSCs from the cell bank for differentiation into IVD cells. Therefore, multiple alternative therapeutic options should be considered if a refined protocol for the differentiation of MSCs into IVD cells is established. In this study, we comprehensively reviewed the molecules, scaffolds, and environmental factors that facilitate the differentiation of MSCs into IVD cells for regenerative therapies for IDD.

TAK-715 alleviated IL-1β-induced apoptosis and ECM degradation in nucleus pulposus cells and attenuated intervertebral disc degeneration ex vivo and in vivo

BACKGROUND

Intervertebral disc degeneration (IDD) is one of the most common disorders related to the spine. Inflammation, apoptosis and extracellular matrix (ECM) degradation contribute to disc degeneration in nucleus pulposus cells (NPCs). This study focused on the role and mechanism of the p38 inhibitor TAK-715 in intervertebral disc degeneration.

METHODS

NPCs were treated with IL-1β to mimic apoptosis, followed by the addition of TAK-715. It was determined that apoptosis, inflammatory mediators (COX-2), inflammatory cytokines (HMGB1), and ECM components (collagen II, MMP9, ADAMTS5, and MMP3) existed in NPCs. In addition, the p38MAPK signaling pathways were examined. The role of TAK-715 in vivo was determined by acupuncture-induced intervertebral disc degeneration. Following an intradiscal injection of TAK-715, MRI and a histopathological analysis were conducted to assess the degree of degeneration.

RESULTS

IL-1β-induced apoptosis was alleviated by TAK-715 in vitro, and antiapoptotic proteins were upregulated. Furthermore, TAK-715 blocked IL-1β-induced inflammatory mediator production (COX-2) and inflammatory cytokine production (HMGB1) and degraded the ECM (collagen II, MMP9, ADAMTS5, and MMP3). By inhibiting the phosphorylation of p38, TAK-715 exerted its effects. In a rat tail model, TAK-715 ameliorates puncture-induced disc degeneration based on MRI and histopathology evaluations.

CONCLUSION

TAK-715 attenuated intervertebral disc degeneration in vitro and in vivo, suggesting that it might be an effective treatment for IDD.

Intervertebral disc cell fate during aging and degeneration: apoptosis, senescence, and autophagy

Background

Degenerative disc disease, a major cause of low back pain and associated neurological symptoms, is a global health problem with the high morbidity, workforce loss, and socioeconomic burden. The present surgical strategy of disc resection and/or spinal fusion results in the functional loss of load, shock absorption, and movement; therefore, the development of new biological therapies is demanded. This achievement requires the understanding of intervertebral disc cell fate during aging and degeneration.

Methods

Literature review was performed to clarify the current concepts and future perspectives of disc cell fate, focused on apoptosis, senescence, and autophagy.

Results

The intervertebral disc has a complex structure with the nucleus pulposus (NP), annulus fibrosus (AF), and cartilage endplates. While the AF arises from the mesenchyme, the NP originates from the notochord. Human disc NP notochordal phenotype disappears in adolescence, accompanied with cell death induction and chondrocyte proliferation. Discs morphologically and biochemically degenerate from early childhood as well, thereby suggesting a possible involvement of cell fate including age-related phenotypic changes in the disease process. As the disc is the largest avascular organ in the body, nutrient deprivation is a suspected contributor to degeneration. During aging and degeneration, disc cells undergo senescence, irreversible growth arrest, producing proinflammatory cytokines and matrix-degradative enzymes. Excessive stress ultimately leads to programmed cell death including apoptosis, necroptosis, pyroptosis, and ferroptosis. Autophagy, the intracellular degradation and recycling system, plays a role in maintaining cell homeostasis. While the incidence of apoptosis and senescence increases with age and degeneration severity, autophagy can be activated earlier, in response to limited nutrition and inflammation, but impaired in aged, degenerated discs. The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) is a signal integrator to determine disc cell fate.

Conclusions

Cell fate and microenvironmental regulation by modulating PI3K/Akt/mTOR signaling is a potential biological treatment for degenerative disc disease.

Injection of Ultra-Purified Stem Cells with Sodium Alginate Reduces Discogenic Pain in a Rat Model

Intervertebral disc (IVD) degeneration is a major cause of low back pain. However, treatments directly approaching the etiology of IVD degeneration and discogenic pain are not yet established. We previously demonstrated that intradiscal implantation of cell-free bioresorbable ultra-purified alginate (UPAL) gel promotes tissue repair and reduces discogenic pain, and a combination of ultra-purified, Good Manufacturing Practice (GMP)-compliant, human bone marrow mesenchymal stem cells (rapidly expanding clones; RECs), and the UPAL gel increasingly enhanced IVD regeneration in animal models. This study investigated the therapeutic efficacy of injecting a mixture of REC and UPAL non-gelling solution for discogenic pain and IVD regeneration in a rat caudal nucleus pulposus punch model. REC and UPAL mixture and UPAL alone suppressed not only the expression of TNF-α, IL-6, and TrkA (p < 0.01, respectively), but also IVD degeneration and nociceptive behavior compared to punching alone (p < 0.01, respectively). Furthermore, REC and UPAL mixture suppressed these expression levels and nociceptive behavior compared to UPAL alone (p < 0.01, respectively). These results suggest that this minimally invasive treatment strategy with a single injection may be applied to treat discogenic pain and as a regenerative therapy.

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.

Intervertebral disc cell chondroptosis elicits neutrophil response in Staphylococcus aureus spondylodiscitis

To understand the pathophysiology of spondylodiscitis due to Staphylococcus aureus, an emerging infectious disease of the intervertebral disc (IVD) and vertebral body with a high complication rate, we combined clinical insights and experimental approaches. Clinical data and histological material of nine patients suffering from S. aureus spondylodiscitis were retrospectively collected at a single center. To mirror the clinical findings experimentally, we developed a novel porcine ex vivo model mimicking acute S. aureus spondylodiscitis and assessed the interaction between S. aureus and IVD cells within their native environment. In addition, the inflammatory features underlying this interaction were assessed in primary human IVD cells. Finally, mirroring the clinical findings, we assessed primary human neutrophils for their ability to respond to secreted inflammatory modulators of IVD cells upon the S. aureus challenge. Acute S. aureus spondylodiscitis in patients was characterized by tissue necrosis and neutrophil infiltration. Additionally, the presence of empty IVD cells’ lacunae was observed. This was mirrored in the ex vivo porcine model, where S. aureus induced extensive IVD cell death, leading to empty lacunae. Concomitant engagement of the apoptotic and pyroptotic cell death pathways was observed in primary human IVD cells, resulting in cytokine release. Among the released cytokines, functionally intact neutrophil-priming as well as broad pro- and anti-inflammatory cytokines which are known for their involvement in IVD degeneration were found. In patients as well as ex vivo in a novel porcine model, S. aureus IVD infection caused IVD cell death, resulting in empty lacunae, which was accompanied by the release of inflammatory markers and recruitment of neutrophils. These findings offer valuable insights into the important role of inflammatory IVD cell death during spondylodiscitis and potential future therapeutic approaches.

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

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

Biomaterials and Cell-Based Regenerative Therapies for Intervertebral Disc Degeneration with a Focus on Biological and Biomechanical Functional Repair: Targeting Treatments for Disc Herniation

Intervertebral disc (IVD) degeneration is a common cause of low back pain and most spinal disorders. As IVD degeneration is a major obstacle to the healthy life of so many individuals, it is a major issue that needs to be overcome. Currently, there is no clinical treatment for the regeneration of degenerated IVDs. However, recent advances in regenerative medicine and tissue engineering suggest the potential of cell-based and/or biomaterial-based IVD regeneration therapies. These treatments may be indicated for patients with IVDs in the intermediate degenerative stage, a point where the number of viable cells decreases, and the structural integrity of the disc begins to collapse. However, there are many biological, biomechanical, and clinical challenges that must be overcome before the clinical application of these IVD regeneration therapies can be realized. This review summarizes the basic research and clinical trials literature on cell-based and biomaterial-based IVD regenerative therapies and outlines the important role of these strategies in regenerative treatment for IVD degenerative diseases, especially disc herniation.

Combination of ultra-purified stem cells with an in situ-forming bioresorbable gel enhances intervertebral disc regeneration

Background

Lumbar intervertebral disc (IVD) herniations are associated with significant disability. Discectomy is the conventional treatment option for IVD herniations but causes a defect in the IVD, which has low self-repair ability, thereby representing a risk of further IVD degeneration. An acellular, bioresorbable, and good manufacturing practice (GMP)-compliant in situ-forming gel, which corrects discectomy-associated IVD defects and prevents further IVD degeneration had been developed. However, this acellular matrix-based strategy has certain limitations, particularly in elderly patients, whose tissues have low self-repair ability. The aim of this study was to investigate the therapeutic efficacy of using a combination of newly-developed, ultra-purified, GMP-compliant, human bone marrow mesenchymal stem cells (rapidly expanding clones; RECs) and the gel for IVD regeneration after discectomy in a sheep model of severe IVD degeneration.

Methods

RECs and nucleus pulposus cells (NPCs) were co-cultured in the gel. In addition, RECs combined with the gel were implanted into IVDs following discectomy in sheep with degenerated IVDs.

Findings

Gene expression of NPC markers, growth factors, and extracellular matrix increased significantly in the co-culture compared to that in each mono-culture. The REC and gel combination enhanced IVD regeneration after discectomy (up to 24 weeks) in the severe IVD degeneration sheep model.

Interpretation

These findings demonstrate the translational potential of the combination of RECs with an in situ-forming gel for the treatment of herniations in degenerative human IVDs.

Funding

Ministry of Education, Culture, Sports, Science, and Technology of Japan, Japan Agency for Medical Research and Development, and the Mochida Pharmaceutical Co., Ltd.

Causes of and Molecular Targets for the Treatment of Intervertebral Disc Degeneration: A Review

Intervertebral disc degeneration (IVDD) is a pathological condition that can lead to intractable back pain or secondary neurological deficits. There is no fundamental cure for this condition, and current treatments focus on alleviating symptoms indirectly. Numerous studies have been performed to date, and the major strategy for all treatments of IVDD is to prevent cell loss due to programmed or regulated cell death. Accumulating evidence suggests that several types of cell death other than apoptosis, including necroptosis, pyroptosis, and ferroptosis, are also involved in IVDD. In this study, we discuss the molecular pathway of each type of cell death and review the literature that has identified their role in IVDD. We also summarize the recent advances in targeted therapy at the RNA level, including RNA modulations through RNA interference and regulation of non-coding RNAs, for preventing cell death and subsequent IVDD. Therefore, we review the causes and possible therapeutic targets for RNA intervention and discuss the future direction of this research field.

Bibliometric Analysis of Functional Magnetic Resonance Imaging Studies on Acupuncture Analgesia Over the Past 20 Years

Background

Researches on the central mechanisms of acupuncture analgesia have been widely conducted worldwide. However, there is no bibliometric analysis of functional magnetic resonance imaging (fMRI) studies on acupuncture analgesia. This study visualized the current status, hot spots and frontiers of fMRI studies on acupuncture analgesia in the past 20 years to provide a theoretical basis for its clinical application.

Methods

All publications were obtained from Science Citation Index-Expanded (SCI-E) of Web of Science (WOS). We used CiteSpace to analyze publications, journals, cited journals, authors, cited authors, institutions, countries, references, and keywords. We also analyzed collaborative network maps and co-occurrence network maps.

Results

We retrieved a total of 797 articles. Regarding the volume of publications, the total number of annual publications showed a fluctuating but overall increasing trend. Evidence-based Complementary and Alternative Medicine (21 articles) was the most productive journal, and Pain (225 articles) was the most cited journal. The most productive author was Qin W (16 articles), and the most co-cited author was Hui KKS (111). The most prolific institution and country were Massachusetts General Hospital (34 articles) and USA (212 articles). “Pain” was the top-ranked for keyword frequency and centrality. “Functional connectivity” was the frontier hotspot for 2018–2021.

Conclusion

First, fMRI researches on acupuncture analgesia involved several countries (regions) and institutions, mainly located in the USA, China and Korea, and most of them were universities. In addition, the USA was a major contributor in this field. Second, in terms of disciplinary distribution, the literatures were mainly from clinical neurology, neuroscience, and radiology nuclear medicine medical imaging. Third, the keyword co-occurrence analysis showed that the hot keywords included pain, fMRI, and lower back pain. Fourth, through keyword clustering analysis, the hot disease was found to be lower back pain, and the hot contents were acupuncture specificity and frequency specificity. Fifth, a timeline analysis of the references identified that chronic low back pain and specificity will remain a hot topic for future research.

Network Pharmacology and Experimental Validation to Reveal the Pharmacological Mechanisms of Liuwei Dihuang Decoction Against Intervertebral Disc Degeneration

Purpose

To explore the pharmacological mechanisms of Liuwei Dihuang Decoction (LWDHD) against intervertebral disc (IVD) degeneration (IVDD) via network pharmacology analysis combined with experimental validation.

Methods

First, active ingredients and related targets of LWDHD, as well as related genes of IVDD, were collected from public databases. The protein–protein interaction (PPI) network, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analyses were performed to predict the core targets and pathways of LWDHD against IVDD. Secondly, the IVDD model of mice treated with LWDHD was selected to validate the major targets predicted by network pharmacology.

Results

By searching the intersection of the active ingredient targets and IVDD targets, a total of 110 targets matched the related targets of 30 active ingredients in LWDHD and IVDD were retrieved. PPI network analysis indicated that 17 targets, including Caspase-3, IL-1β, P53, etc., were hub targets. GO and KEGG enrichment analyses showed that the apoptosis pathway was enriched by multiple targets and served as the target for in vivo experimental study validation. The results of animal experiments revealed that LWDHD administration not only restored the decrease in disc height and abnormal degradation of matrix metabolism in IVDD mice but also reversed the high expression of Bax, Caspase-3, IL-1β, P53, and low expression of Bcl-2, thereby inhibiting the apoptosis of IVD tissue and ameliorating the progression of IVDD.

Conclusion

Using a comprehensive network pharmacology approach, our findings predicted the active ingredients and potential targets of LWDHD intervention for IVDD, and some major target proteins involved in the predictive signaling pathway were validated experimentally, which gave us a new understanding of the pharmacological mechanism of LWDHD in treating IVDD at the comprehensive level.

The REDD1/TXNIP Complex Accelerates Oxidative Stress-Induced Apoptosis of Nucleus Pulposus Cells through the Mitochondrial Pathway

The death of nucleus pulposus (NP) cells is an important cause of intervertebral disc (IVD) degeneration. Redox disturbance caused by dysfunctional mitochondria has been considered as a vital risk for NP cell survival. It is valuable to identify key proteins maintaining mitochondrial function in NP cells. A previous study found that regulated in development and DNA damage response 1 (REDD1) are upregulated during intervertebral disc degeneration and that REDD1 can cause NP cell apoptosis. Thus, the present study further explores the effect of REDD1 on IVD degeneration. Our results showed that REDD1 promotes NP cell apoptosis via the mitochondrial pathway. Importantly, REDD1 formed a complex with TXNIP to strengthen its own action, and the combination was consolidated under H₂O₂-induced oxidative stress. The combined inhibition of the REDD1/TXNIP complex was better than that of REDD1 or TXNIP alone in restoring cell proliferation and accelerating apoptosis. Moreover, p53 acts as the transcription factor of REDD1 to regulate the REDD1/TXNIP complex under oxidative stress. Altogether, our results demonstrated that the REDD1/TXNIP complex mediated H₂O₂-induced human NP cell apoptosis and IVD degeneration through the mitochondrial pathway. Interferences on these sites to achieve mitochondrial redox homeostasis may be a novel therapeutic strategy for oxidative stress-associated IVD degeneration.

Exploratory clinical trial on the safety and capability of dMD-001 in lumbar disc herniation: Study protocol for a first-in-human pilot study

Herniated nucleus pulposus (NP), one of the most common diseases of the spine, is surgically treated by removing the sequestered NP. However, intervertebral disc (IVD) defects may remain after discectomy, leading to inadequate tissue healing and predisposing patients to IVD degeneration. An acellular, bioresorbable, ultra-purified alginate (UPAL) gel (dMD-001) implantation system can be used to fill any IVD defects in order to prevent IVD degeneration after discectomy. This first-in-human pilot study aims to determine the feasibility, safety, and perceived patient response to a combined treatment involving discectomy and UPAL gel implantation for herniated NP. We designed a one-arm, double-centre, open-label, pilot trial. The study started in November 2018 and will run until a sample of 40 suitable participants is established. Patients aged 20-49 years, diagnosed with isolated lumbar IVD herniation and scheduled for discectomy represent suitable candidates. All eligible participants who provide informed consent undergo standard discectomy followed by UPAL gel implantation. The primary outcomes of the trial will be the feasibility and safety of the procedure. Secondary outcomes will include self-assessed clinical scores and magnetic resonance imaging-based measures of morphological and compositional quality of the IVD tissue. Initial outcomes will be published at 24 weeks. Analysis of feasibility and safety will be performed using descriptive statistics. Both intention-to-treat and per-protocol analyses of treatment trends of effectiveness will be conducted.

Long non-coding RNA RP11-81H3.2 suppresses apoptosis by targeting microRNA-1539/COL2A1 in human nucleus pulposus cells

Intervertebral disk degeneration (IDD) is a severe health problem that results in lower back pain and disability. Previous evidence has indicated that excessive apoptosis of nucleus pulposus (NP) cell is involved in the occurrence and development of IDD. However, the underlying mechanisms regulating NP cell apoptosis are unclear. The present study aimed to investigate the function of a novel long non-coding RNA RP11-81H3.2 in modulating NP cell apoptosis and the potential underlying mechanisms. The results demonstrated that the RP11-81H3.2 expression levels were significantly decreased in NP tissues from patients with IDD compared with those from healthy controls, and that lower expression levels were associated with higher-grade disk degeneration. Functionally, RP11-81H3.2 silencing promoted apoptosis and decreased the viability of NP cells derived from tissue samples of patients with IDD, whereas RP11-81H3.2 overexpression induced opposite effects. Bioinformatics analysis, luciferase assays and reverse transcription-quantitative PCR revealed that microRNA (miR)-1539 was a direct target of RP11-81H3.2. A mechanistic analysis demonstrated that RP11-81H3.2 functioned as an RNA sink to downregulate miR-1539, which led to the upregulation of collagen type 2 α 1 chain (COL2A1), a target of miR-1539. Collectively, the present results suggested that lower RP11-81H3.2 expression levels were associated with higher-grade IDD, and that RP11-81H3.2 inhibited NP cell apoptosis by decreasing the levels of miR-1539 to increase COL2A1 expression levels. The present study identified a beneficial role of RP11-81H3.2 against NP cell apoptosis.

Bone Marrow Aspirate Concentrate Combined with in Situ Forming Bioresorbable Gel Enhances Intervertebral Disc Regeneration in Rabbits

BACKGROUND

The current surgical procedure of choice for intervertebral disc (IVD) herniation is discectomy, which induces postoperative IVD degeneration. Thus, cell-based therapies, as a 1-step simple procedure, are desired because of the poor capacity of IVDs for self-repair. The aim of this study was to investigate the repair efficacy of ultra-purified alginate (UPAL) gels containing bone marrow aspirate concentrate (BMAC) for the treatment of discectomy-associated IVD degeneration in rabbits.

METHODS

The mechanical properties of 3 types of gels-UPAL, UPAL containing bone marrow-derived mesenchymal stem cells (BMSCs), and UPAL containing BMAC-were evaluated. Forty rabbits were assigned to 5 groups: intact control, discectomy (to make the cavity), UPAL (implantation of the UPAL gel after discectomy), BMSCs-UPAL (implantation of a combination of autogenic BMSCs and UPAL gel after discectomy), and BMAC-UPAL (implantation of a combination of BMAC and UPAL gel after discectomy). The gels were implanted at 4 weeks after induction of IVD degeneration. At 4 and 12 weeks, magnetic resonance imaging (MRI) as well as histological and immunohistochemical analyses were performed to analyze IVD degeneration qualitatively and the viability of the implanted cells.

RESULTS

There was no significant difference among the 3 types of gels in terms of the results of unconfined compression tests. The implanted cells survived for 12 weeks. The histological grades of the BMSCs-UPAL (mean and standard deviation, 2.50 ± 0.53; p < 0.001) and BMAC-UPAL (2.75 ± 0.64, p = 0.001) showed them to be more effective in preventing degeneration than UPAL gel alone (3.63 ± 0.52). The effectiveness of BMAC-UPAL was not significantly different from that of BMSCs-UPAL, except with respect to type-II collagen synthesis.

CONCLUSIONS

BMAC-UPAL significantly enhanced the repair of IVD defects created by discectomy. This approach could be an effective therapeutic strategy owing to its simplicity and cost-effectiveness compared with cell therapy using culture-expanded BMSCs.

CLINICAL RELEVANCE

Local administration of the BMAC combined with UPAL gel could be an effective therapeutic strategy to enhance IVD repair after discectomy.

Inhibition of LRRK2 restores parkin-mediated mitophagy and attenuates intervertebral disc degeneration

OBJECTIVE

To elucidate the role of LRRK2 in intervertebral disc degeneration (IDD) as well as its mitophagy regulation mechanism.

METHODS

The expression of LRRK2 in human degenerative nucleus pulposus tissues as well as in oxidative stress-induced rat nucleus pulposus cells (NPCs) was detected by western blot. LRRK2 was knocked down in NPCs by lentivirus (LV)-shLRRK2 transfection; apoptosis and mitophagy were assessed by western blot, TUNEL assay, immunofluorescence staining and mitophagy detection assay in LRRK2-deficient NPCs under oxidative stress. After knockdown of Parkin in NPCs with siRNA transfection, apoptosis and mitophagy were further assessed. In puncture-induced rat IDD model, X-ray, MRI, hematoxylin-eosin (HE) and Safranin O-Fast green (SO) staining were performed to evaluate the therapeutic effects of LV-shLRRK2 on IDD.

RESULTS

We found that the expression of LRRK2 was increased in degenerative NPCs both in vivo and in vitro. LRRK2 deficiency significantly suppressed oxidative stress-induced mitochondria-dependent apoptosis in NPCs; meanwhile, mitophagy was promoted. However, these effects were abolished by the mitophagy inhibitor, suggesting the effect of LRRK2 on apoptosis in NPCs is mitophagy-dependent. Furthermore, Parkin knockdown study showed that LRRK2 deficiency activated mitophagy by recruiting Parkin. In vivo study demonstrated that LRRK2 inhibition ameliorated IDD in rats.

CONCLUSIONS

The results revealed that LRRK2 is involved in the pathogenesis of IDD, while knockdown of LRRK2 inhibits oxidative stress-induced apoptosis through mitophagy. Thus, inhibition of LRRK2 may be a promising therapeutic strategy for IDD.

Cellular transplantation and platelet-rich plasma injections for discogenic pain: a contemporary review

Degenerative disc disease (DDD) is the leading cause of chronic back pain. It is a pathologic condition associated with aging and is believed to result from catabolic excess in the intervertebral discs' (IVD) extracellular matrix. Two new treatment options are intradiscal cellular transplantation and growth factor therapy. Recent investigations on the use of these therapies are discussed and compared with emerging evidence supporting novel cellular injections. At present, human and animal studies provide a compelling rationale for the use of cellular injections in the treatment of discogenic pain. Since DDD results from the IVD extracellular matrix's unmitigated catabolism, cellular injections are used to induce regeneration and homeostasis in the IVD. Here, we review intervertebral disc anatomy, DDD pathophysiology and clinical considerations, as well as the current and emerging literature investigating outcomes associated with cellular transplantation and platelet-rich plasma for discogenic pain. Further high-quality trials are certainly warranted.

Ultra-purified alginate gel implantation decreases inflammatory cytokine levels, prevents intervertebral disc degeneration, and reduces acute pain after discectomy

Lumbar intervertebral disc (IVD) herniation causes severe low back pain (LBP), which results in substantial financial and emotional strains. Despite the effectiveness of discectomy, there is no existing treatment for post-operative LBP induced by progressive IVD degeneration. Two key factors of LBP are intradiscal inflammation, indicated by tumour necrosis factor alpha (TNF-α) and interleukin-6 (IL-6), and sensory nerve ingrowth into the inner layer of the annulus fibrosus, triggered by nerve growth factor/high-affinity tyrosine kinase A (TrkA) signalling. In an animal models of discectomy, the bioresorbable ultra-purified alginate (UPAL) gel with an extremely low-toxicity has been effective in acellular tissue repair. We aimed to investigate whether UPAL gel can alleviate LBP using a rat nucleus pulposus (NP) punch model and a rabbit NP aspirate model. In both models, we assessed TNF-α and IL-6 production and TrkA expression within the IVD by immunohistochemistry. Further, histological analysis and behavioural nociception assay were conducted in the rat model. UPAL gel implantation suppressed TNF-α and IL-6 production, downregulated TrkA expression, inhibited IVD degeneration, and reduced nociceptive behaviour. Our results suggest the potential of UPAL gel implantation as an innovative treatment for IVD herniation by reducing LBP and preventing IVD degeneration after discectomy.

Mitochondrial Dysfunction in Intervertebral Disc Degeneration: From Pathogenesis to Therapeutic Target

Mitochondria are cytosolic organelles essential for cellular function and survival. The function of mitochondria is maintained by mitochondrial quality control systems including mitochondrial fission and fusion to adapt the altered environment and mitophagy for removal of damaged mitochondria. Mitochondrial dysfunction is closely involved in aging-related diseases. Intervertebral disc (IVD) degeneration, an aging-associated process, is the major contributor to low back pain. Growing evidence has suggested that the mitochondrial function in IVD cells is severely compromised during the degenerative process of IVD, and dysfunctional mitochondria along with impaired mitochondrial dynamics and mitophagy cause a series of cascade reactions that have been implicated in increased oxidative stress, senescence, matrix catabolism, and apoptosis of IVD cells, thereby contributing to the degeneration of IVD. Accordingly, therapies that target mitochondrial dysfunction and related mechanisms, such as ROS generation, mitophagy, and specific molecules and signaling, hold great promise. The present review summarizes the current state of the role of mitochondrial dysfunction in the pathophysiology of IVD degeneration and potential therapeutic strategies that could be developed.

Non-viral Gene Delivery Methods for Bone and Joints

Viral carrier transport efficiency of gene delivery is high, depending on the type of vector. However, viral delivery poses significant safety concerns such as inefficient/unpredictable reprogramming outcomes, genomic integration, as well as unwarranted immune responses and toxicity. Thus, non-viral gene delivery methods are more feasible for translation as these allow safer delivery of genes and can modulate gene expression transiently both in vivo, ex vivo, and in vitro. Based on current studies, the efficiency of these technologies appears to be more limited, but they are appealing for clinical translation. This review presents a summary of recent advancements in orthopedics, where primarily bone and joints from the musculoskeletal apparatus were targeted. In connective tissues, which are known to have a poor healing capacity, and have a relatively low cell-density, i.e., articular cartilage, bone, and the intervertebral disk (IVD) several approaches have recently been undertaken. We provide a brief overview of the existing technologies, using nano-spheres/engineered vesicles, lipofection, and in vivo electroporation. Here, delivery for microRNA (miRNA), and silencing RNA (siRNA) and DNA plasmids will be discussed. Recent studies will be summarized that aimed to improve regeneration of these tissues, involving the delivery of bone morphogenic proteins (BMPs), such as BMP2 for improvement of bone healing. For articular cartilage/osteochondral junction, non-viral methods concentrate on targeted delivery to chondrocytes or MSCs for tissue engineering-based approaches. For the IVD, growth factors such as GDF5 or GDF6 or developmental transcription factors such as Brachyury or FOXF1 seem to be of high clinical interest. However, the most efficient method of gene transfer is still elusive, as several preclinical studies have reported many different non-viral methods and clinical translation of these techniques still needs to be validated. Here we discuss the non-viral methods applied for bone and joint and propose methods that can be promising in clinical use.

Animal models of regenerative medicine for biological treatment approaches of degenerative disc diseases

Degenerative disc disease (DDD) is a painful, chronic and progressive disease, which is characterized by inflammation, structural and biological deterioration of the intervertebral disc (IVD) tissues. DDD is specified as cell-, age-, and genetic-dependent degenerative process that can be accelerated by environmental factors. It is one of the major causes of chronic back pain and disability affecting millions of people globally. Current treatment options, such as physical rehabilitation, pain management, and surgical intervention, can provide only temporary pain relief. Different animal models have been used to study the process of IVD degeneration and develop therapeutic options that may restore the structure and function of degenerative discs. Several research works have depicted considerable progress in understanding the biological basis of disc degeneration and the therapeutic potentials of cell transplantation, gene therapy, applications of supporting biomaterials and bioactive factors, or a combination thereof. Since animal models play increasingly significant roles in treatment approaches of DDD, we conducted an electronic database search on Medline through June 2020 to identify, compare, and discuss publications regarding biological therapeutic approaches of DDD that based on intradiscal treatment strategies. We provide an up-to-date overview of biological treatment strategies in animal models including mouse, rat, rabbit, porcine, bovine, ovine, caprine, canine, and primate models. Although no animal model could profoundly reproduce the clinical conditions in humans; animal models have played important roles in specifying our knowledge about the pathophysiology of DDD. They are crucial for developing new therapy approaches for clinical applications.

Drug delivery in intervertebral disc degeneration and osteoarthritis: Selecting the optimal platform for the delivery of disease-modifying agents

Osteoarthritis (OA) and intervertebral disc degeneration (IVDD) as major cause of chronic low back pain represent the most common degenerative joint pathologies and are leading causes of pain and disability in adults. Articular cartilage (AC) and intervertebral discs are cartilaginous tissues with a similar biochemical composition and pathophysiological aspects of degeneration. Although treatments directed at reversing these conditions are yet to be developed, many promising disease-modifying drug candidates are currently under investigation. Given the localized nature of these chronic diseases, drug delivery systems have the potential to enhance therapeutic outcomes by providing controlled and targeted release of bioactives, minimizing the number of injections needed and increasing drug concentration in the affected areas. This review provides a comprehensive overview of the currently most promising disease-modifying drugs as well as potential drug delivery systems for OA and IVDD therapy.

Resveratrol protects against apoptosis induced by interleukin-1β in nucleus pulposus cells via activating mTOR/caspase-3 and GSK-3β/caspase-3 pathways

Objective: The purpose of the present study was to investigate the specific downstream signaling pathway mediated by PI3K/Akt in resveratrol (RES) anti-apoptosis of nucleus pulposus cells (NPCs).

Materials and methods: Human NPCs were cultured and divided into six groups. Interleukin (IL)-1β was used to induce apoptosis and RES to inhibit apoptosis. Fluorescence-activated cell sorting (FACS) analysis was used to test apoptotic incidence of NPCs, cell counting kit-8 (CCK-8) assay was performed to detect cell viability, The expression level of caspase-3 mRNA was detected by RT-qPCR, and protein levels were determined by Western blot.

Results: Flow cytometry analysis showed that IL-1β increased the apoptosis rate of NPCs in each group, and RES significantly decreased the apoptosis rate, while rapamycin (RAPA) and SB216763 inhibited the effect of RES and increased the apoptosis rate again. Similarly, CCK-8 showed that IL-1β decreased activity of NPCs in each group, while RES increased cell activity, RAPA and SB216763 inhibited the effect of RES and decreased cell activity. RT-qPCR results showed IL-1β significantly increased the level of caspase-3 expression, but it was significantly decreased by using RES, RAPA and SB216763 respectively attenuated effects of RES. Western blot results showed that activated caspase-3 was inhibited by RES effect, and was up-regulated again after the addition of RAPA and SB216763. In addition, p-mTOR and p-GSK-3β were up-regulated by RES and down-regulated by RAPA and SB216763.

Conclusion: RES can inhibit apoptosis induced by IL-1β in human NPCs. PI3K/Akt/mTOR/caspase-3 and PI3K/Akt/GSK-3β/caspase-3 pathways are potential mechanisms underlying this process.

Gene Therapy Approach for Intervertebral Disc Degeneration: An Update

Intervertebral disc degeneration is the primary cause of back pain and associated with neurological disorders including radiculopathy, myelopathy, and paralysis. The currently available surgical treatments predominantly include the excision of pathological discs, resulting in the function loss, immobilization, and potential additional complications due to the altered biomechanics. Gene therapy approach involves gene transfer into cells, affects RNA and protein synthesis of the encoded genes in the recipient cells, and facilitates biological treatment. Relatively long-exerting therapeutic effects by gene therapy are potentially advantageous to treat slow progressive degenerative disc disease. In gene therapy, the delivery method and selection of target gene(s) are essential. Although gene therapy was first mediated by viral vectors, technological progress has enabled to apply nonviral vectors and polyplex micelles for the disc. While RNA interference successfully provides specific downregulation of multiple genes in the disc, clustered regularly interspaced short palindromic repeats (CRISPR) system has increased attention to alter the process of intervertebral disc degeneration. Then, more recent findings of our studies have suggested autophagy, the intracellular self-digestion, and recycling system under the negative regulation by the mammalian target of rapamycin (mTOR), as a gene therapy target in the disc. Here we briefly review backgrounds and applications of gene therapy for the disc, introducing strategies of autophagy and mTOR signaling modulation through selective RNA interference.

Bone marrow mesenchymal stem cells combined with ultra-purified alginate gel as a regenerative therapeutic strategy after discectomy for degenerated intervertebral discs

BACKGROUND

Because the regenerative ability of intervertebral discs (IVDs) is restricted, defects caused by discectomy may induce insufficient tissue repair leading to further IVD degeneration. An acellular bioresorbable biomaterial based on ultra-purified alginate (UPAL) gel was developed to fill the IVD cavity and prevent IVD degeneration. However, an acellular matrix-based strategy may have limitations, particularly in the elderly population, who exhibit low self-repair capability. Therefore, further translational studies involving product combinations, such as UPAL gel plus bone marrow-derived mesenchymal stem cells (BMSCs), are required to evaluate the regenerative effects of BMSCs embedded in UPAL gel on degenerated IVDs.

METHODS

Rabbit BMSCs and nucleus pulposus cells (NPCs) were co-cultured in a three-dimensional (3D) system in UPAL gel. In addition, rabbit or human BMSCs combined with UPAL gel were implanted into IVDs following partial discectomy in rabbits with degenerated IVDs.

FINDINGS

Gene expression of NPC markers, growth factors, and extracellular matrix was significantly increased in the NPC and BMSC 3D co-culture compared to that in each 3D mono-culture. In vivo, whereas UPAL gel alone suppressed IVD degeneration as compared to discectomy, the combination of BMSCs and UPAL gel exerted a more potent effect to induce IVD regeneration. Similar IVD regeneration was observed using human BMSCs.

INTERPRETATION

These findings demonstrate the therapeutic potential of BMSCs combined with UPAL gel as a regenerative strategy following discectomy for degenerated IVDs.

FUNDING

Ministry of Education, Culture, Sports, Science, and Technology of Japan, Japan Agency for Medical Research and Development, and the Mochida Pharmaceutical Co., Ltd.

Intervertebral disc ageing and degeneration: The antiapoptotic effect of oestrogen

As an important part of the spinal column, the intervertebral disc (IVD) plays an important role in the intervertebral juncture and spinal movement in general. IVD degeneration (IVDD), which mimics disc ageing but at an accelerated rate, is a common and chronic process that results in severe spinal symptoms, such as lower back pain. It is generally assumed that lower back pain caused by IVDD can also develop secondary conditions, including spinal canal stenosis, spinal segmental instability, osteophyte formation, disc herniation and spinal cord and nerve root compression. Over the past few years, many researchers around the world have widely studied the relevance between oestrogen and IVDD, indicating that oestrogen can effectively alleviate IVDD development by inhibiting the apoptosis of IVD cells. Oestrogen can decrease IVD cell apoptosis in multiple ways, including the inhibition of the inflammatory cytokines IL-1β and TNF-α, reducing catabolism because of inhibition of matrix metalloproteinases, upregulating integrin α₂β₁ and IVD anabolism, activating the PI3K/Akt pathway, decreasing oxidative damage and promoting autophagy. In this article, we perform an overview of the literature regarding the antiapoptotic effect of oestrogen in IVDD.

Neurally adjusted ventilatory assist mitigates ventilator-induced diaphragm injury in rabbits

Background

Ventilator-induced diaphragmatic dysfunction is a serious complication associated with higher ICU mortality, prolonged mechanical ventilation, and unsuccessful withdrawal from mechanical ventilation. Although neurally adjusted ventilatory assist (NAVA) could be associated with lower patient-ventilator asynchrony compared with conventional ventilation, its effects on diaphragmatic dysfunction have not yet been well elucidated.

Methods

Twenty Japanese white rabbits were randomly divided into four groups, (1) no ventilation, (2) controlled mechanical ventilation (CMV) with continuous neuromuscular blockade, (3) NAVA, and (4) pressure support ventilation (PSV). Ventilated rabbits had lung injury induced, and mechanical ventilation was continued for 12 h. Respiratory waveforms were continuously recorded, and the asynchronous events measured. Subsequently, the animals were euthanized, and diaphragm and lung tissue were removed, and stained with Hematoxylin-Eosin to evaluate the extent of lung injury. The myofiber cross-sectional area of the diaphragm was evaluated under the adenosine triphosphatase staining, sarcomere disruptions by electron microscopy, apoptotic cell numbers by the TUNEL method, and quantitative analysis of Caspase-3 mRNA expression by real-time polymerase chain reaction.

Results

Physiological index, respiratory parameters, and histologic lung injury were not significantly different among the CMV, NAVA, and PSV. NAVA had lower asynchronous events than PSV (median [interquartile range], NAVA, 1.1 [0–2.2], PSV, 6.8 [3.8–10.0], p = 0.023). No differences were seen in the cross-sectional areas of myofibers between NAVA and PSV, but those of Type 1, 2A, and 2B fibers were lower in CMV compared with NAVA. The area fraction of sarcomere disruptions was lower in NAVA than PSV (NAVA vs PSV; 1.6 [1.5–2.8] vs 3.6 [2.7–4.3], p < 0.001). The proportion of apoptotic cells was lower in NAVA group than in PSV (NAVA vs PSV; 3.5 [2.5–6.4] vs 12.1 [8.9–18.1], p < 0.001). There was a tendency in the decreased expression levels of Caspase-3 mRNA in NAVA groups. Asynchrony Index was a mediator in the relationship between NAVA and sarcomere disruptions.

Conclusions

Preservation of spontaneous breathing using either PSV or NAVA can preserve the cross sectional area of the diaphragm to prevent atrophy. However, NAVA may be superior to PSV in preventing sarcomere injury and apoptosis of myofibrotic cells of the diaphragm, and this effect may be mediated by patient-ventilator asynchrony.

Caspase-3 knockout inhibits intervertebral disc degeneration related to injury but accelerates degeneration related to aging

Approximately 40% of people under 30 and over 90% of people 55 or older suffer from moderate-to-severe levels of degenerative intervertebral disc (IVD) disease in their lumbar spines. Surgical treatments are sometimes effective; however, the treatment of back pain related to IVD degeneration is still a challenge; therefore, new treatments are necessary. Apoptosis may be important in IVD degeneration because suppressing cell apoptosis inside the IVD inhibits degeneration. Caspase-3, the primary effector of apoptosis, may be a key treatment target. We analyzed caspase-3’s role in two different types of IVD degeneration using caspase-3 knockout (Casp-3 KO) mice. Casp-3 KO delayed IVD degeneration in the injury-induced model but accelerated it in the age-induced model. Our results suggest that this is due to different pathological mechanisms of these two types of IVD degeneration. Apoptosis was suppressed in the IVD cells of Casp-3 KO mice, but cellular senescence was enhanced. This would explain why the Casp-3 KO was effective against injury-induced, but not age-related, IVD degeneration. Our results suggest that short-term caspase-3 inhibition could be used to treat injury-induced IVD degeneration.

Critical contribution of RIPK1 mediated mitochondrial dysfunction and oxidative stress to compression-induced rat nucleus pulposus cells necroptosis and apoptosis

The aim of this study was to investigate whether RIPK1 mediated mitochondrial dysfunction and oxidative stress contributed to compression-induced nucleus pulposus (NP) cells necroptosis and apoptosis, together with the interplay relationship between necroptosis and apoptosis in vitro. Rat NP cells underwent various periods of 1.0 MPa compression. To determine whether compression affected mitochondrial function, we evaluated the mitochondrial membrane potential, mitochondrial permeability transition pore (mPTP), mitochondrial ultrastructure and ATP content. Oxidative stress-related indicators reactive oxygen species, superoxide dismutase and malondialdehyde were also assessed. To verify the relevance between oxidative stress and necroptosis together with apoptosis, RIPK1 inhibitor necrostatin-1(Nec-1), mPTP inhibitor cyclosporine A (CsA), antioxidants and small interfering RNA technology were utilized. The results established that compression elicited a time-dependent mitochondrial dysfunction and elevated oxidative stress. Nec-1 and CsA restored mitochondrial function and reduced oxidative stress, which corresponded to decreased necroptosis and apoptosis. CsA down-regulated mitochondrial cyclophilin D expression, but had little effects on RIPK1 expression and pRIPK1 activation. Additionally, we found that Nec-1 largely blocked apoptosis; whereas, the apoptosis inhibitor Z-VAD-FMK increased RIPK1 expression and pRIPK1 activation, and coordinated regulation of necroptosis and apoptosis enabled NP cells survival more efficiently. In contrast to Nec-1, SiRIPK1 exacerbated mitochondrial dysfunction and oxidative stress. In summary, RIPK1-mediated mitochondrial dysfunction and oxidative stress play a crucial role in NP cells necroptosis and apoptosis during compression injury. The synergistic regulation of necroptosis and apoptosis may exert more beneficial effects on NP cells survival, and ultimately delaying or even retarding intervertebral disc degeneration.

Down-regulation of insulin-like growth factor binding protein 5 is involved in intervertebral disc degeneration via the ERK signalling pathway

It is obvious that epigenetic processes influence the evolution of intervertebral disc degeneration (IDD). However, its molecular mechanisms are poorly understood. Therefore, we tested the hypothesis that IGFBP5, a potential regulator of IDD, modulates IDD via the ERK signalling pathway. We showed that IGFBP5 mRNA was significantly down-regulated in degenerative nucleus pulposus (NP) tissues. IGFBP5 was shown to significantly promote NP cell proliferation and inhibit apoptosis in vitro, which was confirmed by MTT, flow cytometry and colony formation assays. Furthermore, IGFBP5 was shown to exert its effects by inhibiting the ERK signalling pathway. The effects induced by IGFBP5 overexpression on NP cells were similar to those induced by treatment with an ERK pathway inhibitor (PD98059). Moreover, qRT-PCR and Western blot analyses were performed to examine the levels of apoptosis-related factors, including Bax, caspase-3 and Bcl2. The silencing of IGFBP5 up-regulated the levels of Bax and caspase-3 and down-regulated the level of Bcl2, thereby contributing to the development of human IDD. Furthermore, these results were confirmed in vivo using an IDD rat model, which showed that the induction of Igfbp5 mRNA expression abrogated the effects of IGFBP5 silencing on intervertebral discs. Overall, our findings elucidate the role of IGFBP5 in the pathogenesis of IDD and provide a potential novel therapeutic target for IDD.

Effects of Intradiscal Injection of Local Anesthetics on Intervertebral Disc Degeneration in Rabbit Degenerated Intervertebral Disc

Analgesic discoblock is widely used for the diagnosis or treatment of discogenic low back pain by injecting local anesthetics. The purpose of this study was to investigate the deleterious effects of local anesthetics on degenerated rabbit intervertebral disks (IVDs) using an organotypic culture model and in vivo long-term follow-up model. To induce IVD degeneration, a rabbit annular puncture model was used. For the organotypic culture model, degenerated IVDs were harvested 1 month after the initial annular puncture and cultured for 3 or 7 days after intradiscal injection of local anesthetics (1% lidocaine and 0.5% bupivacaine). To perform in vivo analysis, local anesthetics were injected into degenerated IVDs, and IVDs were prepared for histological analysis after 6 or 12 months. In the organotypic model, terminal deoxynucleotidyl transferase dUTP nick end labeling-positive nucleus pulposus (NP) cells were significantly increased in the bupivacaine group compared with the other groups. In the in vivo study, the number of NP cells was significantly decreased in the saline and local anesthetics groups compared with the untreated control and puncture-only groups. However, there was no significant difference among the saline, lidocaine, and bupivacaine groups. In addition, histological analysis showed no significant difference of IVD degeneration among the puncture-only, saline, lidocaine, and bupivacaine groups. Although bupivacaine induced apoptotic NP cell death in the organotypic culture model, in vivo observations did not show any definitive proof to suggest that local anesthetics were capable of promoting degeneration in the degenerated IVD, except for pressurized injection-induced damage. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1963-1971, 2019.

Overexpressed IGFBP5 promotes cell proliferation and inhibits apoptosis of nucleus pulposus derived from rats with disc degeneration through inactivating the ERK/MAPK axis

It is previously suggested that insulin-like growth factor binding proteins (IGFBPs) potentially share an association with disc degeneration (DD) that causes back pain. This study aimed at exploring the functional relevance of IGFBP5 in DD by establishing a rat model of DD. The nucleus pulposus (NP) cells were transduced with IGFBP5-shRNA or IGFBP5 overexpression to determine the cellular processes (proliferation, apoptosis, as well as colony formation). The protein levels of apoptosis-related proteins were evaluated. Furthermore, NP cells were treated with the extracellular signal-regulated kinases/mitogen-activated protein kinase (ERK/MAPK) pathway inhibitor (PD98059) followed by measurement of ERK protein level and ERK phosphorylation content. The NP cells showed suppressed proliferation and colony formation ability, yet promoted apoptosis after transfection with IGFBP5-shRNA. It was found that silencing of IGFBP5 could lead to the ERK/MAPK axis activation, as indicated by an elevated ERK protein level and ERK phosphorylation content. However, overexpression of IGFBP5 could reverse all the reaction induced by silenced IGFBP5. These key findings demonstrate that overexpressed IGFBP5 inactivates the ERK/MAPK axis to stimulate the proliferation and inhibit apoptosis of NP cells in a rat model of DD.

Efficiency of dual siRNA-mediated gene therapy for intervertebral disc degeneration (IVDD)

BACKGROUND CONTEXT

One of the common causes of low back pain is intervertebral disc degeneration. The pathophysiology of disc degeneration involves apoptosis of nucleus pulposes cells and degradation of extra cellular matrix (ECM). Caspase 3 plays a central role in apoptosis and the ADAMTS5 (A Disintegrin and Metalloproteinase with Thrombospondin motifs 5) gene plays a critical role in ECM degradation. Hence, we hypothesized that if one can silence these two genes, both apoptosis and ECM degradation can be prevented, thereby preventing the progression and even reverse disc degeneration.

PURPOSE

The purpose of this study is to demonstrate the regenerative potential of small interfering RNA (siRNA) designed against Caspase 3 and ADAMTS5 genes in an in vitro and animal model of disc degeneration.

STUDY DESIGN

In vitro study followed by in vivo study in a rabbit model.

METHODS

In vitro studies were done using the human hepatocellular carcinoma (Hep G2) cell line for validating the efficacy of liposomal siRNA in controlling the expression of genes (Caspase 3 and ADAMTS5). Later, siRNA's validation was done in a rabbit annular punctured model by administering siRNA's individually (Caspase 3 and ADAMTS5) and in combination Caspase3-ADAMTS5) for assessing their synergistic effect in down regulating the gene expression in the degenerative discs. Annular punctured intervertebral discs of the rabbit were injected with siRNA formulations (single and dual) and phosphate buffer saline, one week after initial puncture. Magnetic resonance imaging (MRI) scans were done before and after siRNA treatment (1, 4 and 8 weeks) for assessing the progression of disc degeneration. The histopathology and real time polymerase chain reaction (RT-PCR) studies were done for evaluating their efficacy. We did not receive any funding for conducting the study, and we do not have a conflict of interest with any researchers or scientific groups.

RESULTS

The observations made from both in vitro and in vivo studies indicate the beneficial effects of siRNA formulation in down regulating the expression of Caspase 3 and ADAMTS5 genes. The MRI and histopathological evaluation showed that the disc degeneration was progressive in phosphate buffer saline and AT5-siRNA injected discs but the discs that received Caspase 3-siRNA and dual siRNA (Cas3-AT5-siRNA) formulation showed signs of recovery and regeneration 4 and 8 weeks after injection. The efficacy of siRNA designed against Cas3 and AT5 was also assessed in both in vitro and in vivo experiments by using RT-PCR analysis and the results showed downregulation of Caspase 3 gene in Caspase 3-siRNA group, but there was no significant downregulation of ADAMTS5 gene in ADAMTS5-siRNA group (ie, indicated by fold change). Synergistic effect was observed in the group that received dual siRNA (Cas3-AT5 siRNA) formulation.

CONCLUSIONS

This experiment suggests that intervention by siRNA treatment significantly reduced the extent of apoptosis in the discs.

CLINICAL SIGNIFICANCE

Delivery of siRNA directly into spinal discs has a potential in treating disc degeneration nonsurgically.

RIPK1 suppresses apoptosis mediated by TNF and caspase-3 in intervertebral discs

BACKGROUND

Low back pain has become a serious social and economic burden and the leading cause of disability worldwide. Among a variety of pathophysiological triggers, intervertebral disc (IVD) degeneration plays a primary underlying role in causing such pain. Specifically, multiple independent endplate changes have been implicated in the initiation and progression of IVD degeneration.

METHODS

In this study, we built a signaling network comprising both well-characterized IVD pathology-associated proteins as well as some potentially correlated proteins that have been associated with one or more of the currently known pathology-associated proteins. We then screened for the potential IVD degeneration-associated proteins using patients' normal and degenerative endplate specimens. Short hairpin RNAs for receptor interacting serine/threonine kinase 1 (RIPK1) were constructed to examine the effects of RIPK1 knockdown in primary chondrocyte cells and in animal models of caudal vertebra intervertebral disc degeneration in vivo.

RESULTS

RIPK1 was identified as a potential IVD degeneration-associated protein based on IVD pathology-associated signaling networks and the patients' degenerated endplate specimens. Construction of the short hairpin RNAs was successful, with short-term RIPK1 knockdown triggering inflammation in the primary chondrocytes, while long-term knockdown triggered apoptosis through cleavage of the caspase 3 pathway, down-regulated NF-κB and mitogen-activating protein kinase (MAPK)s cascades, and decreased cell survival and inflammation. Animal models of caudal vertebra intervertebral disc degeneration further demonstrated that apoptosis was induced by up-regulation of tumor necrosis factor (TNF) accompanied by down-regulation of NF-κB and MAPKs cascades that are dependent on caspase and RIPK1.

CONCLUSIONS

These results provide proof-of-concept for developing novel therapies to combat IVD degeneration through interfering with RIPK1-mediated apoptosis signaling pathways especially in patients with RIPK1 abnormality.

Materials for the Spine: Anatomy, Problems, and Solutions

Disc degeneration affects 12% to 35% of a given population, based on genetics, age, gender, and other environmental factors, and usually occurs in the lumbar spine due to heavier loads and more strenuous motions. Degeneration of the extracellular matrix (ECM) within reduces mechanical integrity, shock absorption, and swelling capabilities of the intervertebral disc. When severe enough, the disc can bulge and eventually herniate, leading to pressure build up on the spinal cord. This can cause immense lower back pain in individuals, leading to total medical costs exceeding $100 billion. Current treatment options include both invasive and noninvasive methods, with spinal fusion surgery and total disc replacement (TDR) being the most common invasive procedures. Although these treatments cause pain relief for the majority of patients, multiple challenges arise for each. Therefore, newer tissue engineering methods are being researched to solve the ever-growing problem. This review spans the anatomy of the spine, with an emphasis on the functions and biological aspects of the intervertebral discs, as well as the problems, associated solutions, and future research in the field.

An acellular bioresorbable ultra-purified alginate gel promotes intervertebral disc repair: A preclinical proof-of-concept study

Background

The current surgical procedure of choice for lumbar intervertebral disc (IVD) herniation is discectomy. However, defects within IVD produced upon discectomy may impair tissue healing and predispose patients to subsequent IVD degeneration. This study aimed to investigate whether the use of an acellular bioresorbable ultra-purified alginate (UPAL) gel implantation system is safe and effective as a reparative therapeutic strategy after lumbar discectomy.

Methods

Human IVD cells were cultured in a three-dimensional system in UPAL gel. In addition, lumbar spines of sheep were used for mechanical analysis. Finally, the gel was implanted into IVD after discectomy in rabbits and sheep in vivo.

Findings

The UPAL gel was biocompatible with human IVD cells and promoted extracellular matrix production after discectomy, demonstrating sufficient biomechanical characteristics without material protrusion.

Interpretation

The present results indicate the safety and efficacy of UPAL gels in a large animal model and suggest that these gels represent a novel therapeutic strategy after discectomy in cases of lumbar IVD herniation.

Fund

Grant-in-Aid for the Ministry of Education, Culture, Sports, Science, and Technology of Japan, Japan Agency for Medical Research and Development, and the Mochida Pharmaceutical Co., Ltd.

Rs217727 polymorphism in H19 promotes cell apoptosis by regulating the expressions of H19 and the activation of its downstream signaling pathway

BACKGROUND

The objective of the current study was to explore the role of H19 rs217727 polymorphism in the control of hepatocellular carcinoma (HCC).

METHOD

The Student's t test, Cox regression, and Kaplan-Meier analyses were used to clarify whether the H19 rs217727 polymorphism played an important role in the development of HCC. Real-time polymerase chain reaction (PCR) and western-blot analysis were carried out to measure the levels of H19, microRNA (miR)-675, FAS-associated death domain (FADD), caspase-8, and caspase-3 among H19 CC, CT, and TT groups, as well as in cells transfected with H19/si-H19, or miR-675 mimic/inhibitor. The MTT assay, colony formation assay, and flow cytometry assay were performed to detect the effect of H19/miR-675 on cell viability, cell colony formation, and cell apoptosis.

RESULT

T allele of H19 rs217727 polymorphism apparently increased the survival rate of patients with HCC. Meanwhile, H19 enhanced miR-675 expression but reduced the mRNA and protein levels of FADD, caspase-3, and caspase-8. The T allele of H19 rs217727 polymorphism apparently increased the apoptotic rate of HCC cells. Furthermore, FADD was a virtual target gene of miR-675 with a potential "hit" located in the 3'-untranslated region (UTR) of FADD, whereas H19 inhibited FADD expression via increasing the expression of miR-675. Moreover, H19 upregulated the expression of miR-675 whereas reducing the expression of FADD, caspase-3, and caspase-8. Finally, H19 and miR-675 promoted cell proliferation and cell colony formation but repressed cell apoptosis.

CONCLUSION

In summary, the above findings demonstrated that the polymorphism of rs217727 in H19 was associated with HCC via the H19/miR-675/FADD/caspase-8/caspase-3/apoptosis signaling pathway.

Nucleus pulposus cell apoptosis is attenuated by CDMP-2 through regulating oxidative damage under the hyperosmotic environment

Disc nucleus pulposus (NP) cell experiences periodic osmolarity alterations during daily activities, which has been proved to affect cell biology in vitro. The present study was aimed to investigate the effects of cartilage-derived morphogenetic protein-2 (CDMP-2) on NP cell apoptosis under the hyperosmolarity culture and the potential mechanism. Isolated rat NP cells were cultured in the in situ-osmolarity medium or hyperosmolarity medium for 3 days. CDMP-2 was added into the hyperosmolarity medium to investigate its effects on NP cell apoptosis. Cell apoptosis rate, caspase-3 activity, gene expression of Bcl-2, Bax, and caspase-3, and protein expression of Bcl-2, Bax, and cleaved caspase-3 were analyzed to evaluate NP cell apoptosis. Additionally, the intracellular reactive oxygen species (ROS) and the total superoxide dismutase (SOD) activity were analyzed to investigate the potential role of oxidative damage in this process. In the hyperosmolarity culture, NP cells showed a significantly increased cell apoptosis rate and caspase-3 activity, an up-regulated expression of Bax and caspase-3/cleaved-caspase-3 and a down-regulated expression of Bcl-2. However, CDMP-2 partly inhibited these effects of hyperosmolarity culture on NP cells. Additionally, the hyperosmolarity culture significantly increased ROS content and decreased the total SOD activity compared with the in situ-osmolarity culture, whereas exogenous CDMP-2 partly decreased the ROS content and increased the total SOD activity in the hyperosmolarity culture. In conclusion, CDMP-2 is effective in attenuating hyperosmolarity environment-induced NP cell apoptosis, and this process may be mediated through inhibiting oxidative stress damage. The present study indicates that CDMP-2 may be helpful to retard hyperosmolarity niche-mediated disc degeneration.

Sirtuin 3-dependent mitochondrial redox homeostasis protects against AGEs-induced intervertebral disc degeneration

Intervertebral disc (IVD) degeneration contributes largely to pathoanatomical and degenerative changes of spinal structure that increase the risk of low back pain. Apoptosis in nucleus pulposus (NP) can aggravate IVD degeneration, and increasing studies have shown that interventions targeting NP cell apoptosis can ameliorate IVD degeneration, exhibiting their potential for use as therapeutic strategies. Recent data have shown that advanced glycation end products (AGEs) accumulate in NP tissues in parallel with the progression of IVD degeneration and form a microenvironment of oxidative stress. This study examined whether AGEs accumulation aggravates NP cell apoptosis and IVD degeneration, and explored the mechanisms underlying these effects. We observed that the viability and proliferation of human NP cells were significantly suppressed by AGEs treatment, mainly due to apoptosis. Furthermore, activation of the mitochondrial apoptosis pathway was detected after AGEs treatment. In addition, the molecular data showed that AGEs could significantly aggravate the generation of mitochondrial reactive oxygen species and prolonged activation of the mitochondrial permeability transition pore, as well as the increased level of Bax protein and decreased level of Bcl-2 protein in mitochondria. These effects could be reduced by antioxidant (2-(2,2,6,6-Tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl) triphenylphosphonium chloride (MitoTEMPO) and Visomitin (SKQ1). Importantly, we identified that impairment of Sirtuin3 (SIRT3) function and the mitochondrial antioxidant network were vital mechanisms in AGEs-induced oxidative stress and secondary human NP cell apoptosis. Finally, based on findings that nicotinamide mononucleotide (NMN) could restore SIRT3 function and rescue human NP cell apoptosis through adenosine monophosphate-activated protein kinase and peroxisome proliferator-activated receptor-γ coactivator 1α (AMPK-PGC-1α) pathway in vitro, we confirmed its protective effect on AGEs-induced IVD degeneration in vivo. In conclusion, our data demonstrate that SIRT3 protects against AGEs-induced human NP cell apoptosis and IVD degeneration. Targeting SIRT3 to improve mitochondrial redox homeostasis may represent a potential therapeutic strategy for attenuating AGEs-associated IVD degeneration.

Resveratrol attenuates mechanical compression-induced nucleus pulposus cell apoptosis through regulating the ERK1/2 signaling pathway in a disc organ culture

BACKGROUND

Nucleus pulposus (NP) cell apoptosis is a typical feature within the degenerative disc. High magnitude compression significantly promotes NP cell apoptosis. Several studies have indicated that resveratrol has protective effects on disc cell's normal biology.

OBJECTIVE

The present study aims to investigate whether resveratrol can attenuate mechanical overloading-induced NP cell apoptosis in a disc organ culture.

METHODS

Isolated porcine discs were cultured in culture chambers of a mechanically active perfusion bioreactor and subjected to a relatively high magnitude compression (1.3 MPa at a frequency of 1.0 Hz for 2 h once per day) for 7 days. Different concentrations (50 and 100 μM) of resveratrol were added into the culture medium to observe the protective effects of resveratrol against NP cell apoptosis under mechanical compression. The noncompressed discs were used as controls.

RESULTS

Similar with the previous studies, this high magnitude compression significantly promoted NP cell apoptosis, reflected by the increased number of terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining-positive NP cells and enzyme (caspase-9 and caspase-3) activity, the up-regulated expression of proapoptotic molecules (Bax and caspase-3/cleaved caspase-3), and down-regulated expression of antiapoptotic molecule (Bcl-2). However, resveratrol partly attenuated NP cell apoptosis under this high magnitude compression in a dose-dependent manner. Additionally, though the ERK1/2 pathway was significantly activated in the mechanical compression group, resveratrol partly attenuated activation of the ERK1/2 pathway under mechanical compression in a dose-dependent manner.

CONCLUSION

Resveratrol attenuates mechanical overloading-induced NP cell apoptosis in a dose-dependent manner, and inhibiting activation of the ERK1/2 pathway may be one potential mechanism behind this regulatory process.

Hydrogen peroxide induces programmed necrosis in rat nucleus pulposus cells through the RIP1/RIP3-PARP-AIF pathway

This study aimed to systematically investigate whether programmed necrosis contributes to H2 O2 -induced nucleus pulposus (NP) cells death and to further explore the underlying mechanism involved. Rat NP cells were subjected to different concentrations of H2 O2 for various time periods. The cell viability was measured using a cell counting kit-8, and the death rate was detected by Hoechst 33258/propidium iodide (PI) staining. The programmed necrosis-related molecules receptor-interacting protein 1 (RIP1), receptor-interacting protein 3 (RIP3), poly (ADP-ribose) polymerase (PARP), and apoptosis inducing factor (AIF) were determined by real-time polymerase chain reaction and Western blotting, respectively. The morphologic and ultrastructural changes were examined by phasecontrast microscopy and transmission electron microscopy (TEM). In addition, the necroptosis inhibitor Necrostatin-1 (Nec-1), the PARP inhibitor diphenyl-benzoquinone (DPQ) and small interfering RNA (siRNA) technology were used to indirectly evaluate programmed necrosis. Our results indicated that H2 O2 induced necrotic morphologic and ultrastructural changes and an elevated PI positive rate in NP cells; these effects were mediated by the upregulation of RIP1 and RIP3, hyperactivation of PARP, and translocation of AIF from mitochondria to nucleus. Additionally, NP cells necrosis was significantly attenuated by Nec-1, DPQ pretreatment and knockdown of RIP3 and AIF, while knockdown of RIP1 produced the opposite effects. In conclusion, these results suggested that under oxidative stress, RIP1/RIP3-mediated programmed necrosis, executed through the PARP-AIF pathway, played an important role in NP cell death. Protective strategies aiming to regulate programmed necrosis may exert a beneficial effect for NP cells survival, and ultimately retard intervertebral disc (IVD) degeneration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1269-1282, 2018.

Simvastatin Inhibits IL-1β-Induced Apoptosis and Extracellular Matrix Degradation by Suppressing the NF-kB and MAPK Pathways in Nucleus Pulposus Cells

Statins are widely used hypocholesterolemic drugs that block the mevalonate pathway. Some studies have shown that statins may have the potential to inhibit intervertebral disk (IVD) degeneration (IDD). Interleukin (IL)-1β, a catabolic cytokine, is a key regulator of IDD. This study aimed to investigate the mechanism underlying the effect of simvastatin on IDD. The viability of nucleus pulposus (NP) cells was determined by the methyl-thiazolyl-tetrazolium (MTT) assay. The apoptosis of NP cells was measured by flow cytometric analysis, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and western blotting of relevant apoptotic proteins. The protein levels of catabolic factors and anabolic factors were determined by western blotting. The cells were stimulated with IL-1β in the absence or presence of simvastatin to investigate the effects on matrix metalloproteinase (MMP)-3, MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4, ADAMTS-5, type II collagen, and aggrecan expression. Our findings indicate that simvastatin considerably inhibited IL-1β-induced apoptosis in NP cells. We also found that simvastatin attenuated IL-1β-induced expression and MMP-3, MMP-13, ADAMTS-4, and ADAMTS-5 activities and also reduced the decrease in type II collagen and aggrecan expression. In addition, simvastatin considerably suppressed the nuclear translocation and activation of nuclear factor-kappa B (NF-KB) by inhibiting p65 phosphorylation and translocation and blocking inhibitor kB-α degradation. It also inhibited MAPK pathway activation by blocking c-Jun N-terminal kinase (JNK), p38, and ERK phosphorylation. The results of our study revealed that simvastatin is a potential agent for IDD prevention and treatment.

Age-related spontaneous lumbar intervertebral disc degeneration in a mouse model

The pathogenesis of intervertebral disc degeneration is unclear, but it is a major cause of several spinal diseases. Animal models have historically provided an appropriate benchmark for understanding the human spine. However, there is little information about when intervertebral disc degeneration begins in the mouse or regarding the relationship between magnetic resonance imaging and histological findings. The aim for this study was to obtain information about age-related spontaneous intervertebral disc degeneration in the mouse lumbar spine using magnetic resonance imaging and a histological score regarding when the intervertebral disc degeneration started and how rapidly it progressed, as well as how our histological score detected the degeneration. The magnetic resonance imaging index yielded a moderate correlation with our Age-related model score. The Pfirrmann grade and magnetic resonance imaging index had moderate correlations with age. However, our Age-related model score had a high correlation with age. Intervertebral disc level was not a significant variable for the severity of disc degeneration. Both Pfirrmann grade and the Age-related model score were higher in the ≥14-month-old group than in the 6-month-old group. The present results indicated that mild but significant intervertebral disc degeneration occurred in 14-month-old mice, and the degree of degeneration progressed slowly, reaching a moderate to severe condition for 22-month-old mice. At least a 14-month follow-up is mandatory for evaluating spontaneous age-related mouse intervertebral disc degeneration. The histological classification score can precisely detect the gradual progression of age-related spontaneous intervertebral disc degeneration in the mouse lumbar spine, and is appropriate for evaluating it. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:224-232, 2018.