Intervertebral disc degeneration and regeneration: a motion segment perspective

Exploring extracellular vesicles as novel therapeutic agents for intervertebral disc degeneration: delivery, applications, and mechanisms

Intervertebral disc degeneration is a multifactorial degenerative disease that poses a significant threat to the health of the elderly population. Current treatments primarily focus on physical therapy, medication, and surgery to alleviate symptoms associated with disc compression but do not address the progression of degeneration. Therefore, this review aimed to explore the potential of extracellular vesicle therapy as a novel preventive strategy to delay degeneration and enhance tissue repair in intervertebral discs. We cover the pathogenic mechanisms underlying intervertebral disc degeneration, including inflammation, apoptosis, pyroptosis, ferroptosis, autophagy dysregulation, and the roles of non-coding RNAs. Subsequently, we discussed the therapeutic potential of extracellular vesicles and their molecular components, such as proteins, RNAs, and lipids, in modulating these pathways to counter intervertebral disc degeneration. We provides a comprehensive review of the significant role of extracellular vesicle cargo in mediating repair mechanisms. It discusses the functional enhancement advantages exhibited by extracellular vesicles under current bioengineering modifications and drug loading. The challenges and future prospects of utilizing extracellular vesicle therapy to treat this degenerative condition are also summarized.

Efficacy of Percutaneous Spinal Endoscopic YESS Technique in Adjacent Segmental Disease Without Severe Instability After Lumbar Fusion Surgery: A Case Series

Background

The adjacent segment disease (ASD) after lumbar fusion is inherently stressed abnormally, and the destruction of bony structures in surgery can further exacerbate that abnormality. The Yeung Endoscopic Spine Surgery (YESS) technique does not destroy facet joints, and therefore it may be a good indication for ASD. However, the efficacy of the YESS technique in ASD patients have not been reported.

Patients and Methods

From January 2018 to May 2023, 13 patients with adjacent spondylolisthesis secondary to lumbar fusion were treated with endoscopic YESS technique surgery. Patients' visual analog score (VAS) and Oswestry disability index (ODI) score were analyzed preoperatively, 3 days postoperatively, and at the final follow-up. Gait analysis parameters and intervertebral height index of patients preoperatively and at 1 year postoperatively were used to objectively quantify patient pain, function, and radiographic changes.

Results

A total of 13 patients, 2 females and 11 males, had single-segment adjacent spondylolisthesis. The patients' VAS and ODI scores at 3 days postoperatively decreased (P<0.05) compared to preoperatively and further decreased (P<0.05) at the final follow-up. There were no infections, wound complications or reoperations. The results of gait analysis showed no statistically significant difference in single-stance time and the gait cycle before and after the patients' surgery (P>0.05), but the patients' velocity, step length, step time, step frequency and stride length were significantly improved at 1-year postoperatively (P<0.05). Intervertebral height loss did not occur in all patients.

Conclusion

In the short term, spinal endoscopic YESS technique markedly improves clinical symptoms and gait parameters in patients with ASD without severe instability after lumbar fusion, while avoiding facet joint destruction and intervertebral height loss. Future studies with larger sample sizes and longer follow-up times are needed to clarify the long-term efficacy.

Design and evaluation of powered lumbar exoskeleton based on human biomechanics

OBJECTIVES

In view of the gradual rejuvenation and acceleration of lumbar spondylosis, a wearable powered lumbar exoskeleton based on a 6-SPU/SP parallel mechanism is designed based on the rehabilitation treatment method of lumbar forward flexion/extension, left/right lateral flexion and rotation.

METHODS

First, the changes in human lumbar muscles are analyzed based on human biomechanics, and then the prototype design of the powered lumbar exoskeleton is implemented, including the mechanical mechanism design, and hardware module design. Finally, the simulation experiment of muscle force and output sensitivity test in the resistive mode are conducted.

RESULTS

The simulation results show that the external oblique muscle can be relieved about 20 % and the iliopsoas muscle can be decreased by 33 % when wearing the powered lumbar exoskeleton in the lateral flexion. The pressure sensors can measure the output force of each actuator in real-time when the resistance force reaches the set value of 15 N at the resistive model.

CONCLUSIONS

The results show that the powered lumbar exoskeleton can assist the human lumbar spine in rehabilitation training of traction, forward flexion and extension, left and right lateral flexion, and rotation. This research provides new ideas for future clinical research.

Efficacy of Naringenin against aging and degeneration of nucleus pulposus cells through IGFBP3 inhibition

Naringenin (NAR), a natural flavonoid, exerts anti-inflammatory and antioxidant pharmacology. However, the pharmacological mechanisms through which NAR prevents and treats intervertebral disc degeneration (IDD) remain unclear. We utilized bioinformatics, machine learning, and network pharmacology to identify shared targets among NAR, senescence, and IDD. Subsequently, molecular docking was conducted to evaluate NAR's binding affinity to common target. Additionally, we used IL-1β to induce senescence and degeneration in nucleus pulposus cells (NPCs) and conducted a series of cellular assays, including immunoblotting, immunofluorescence, β-galactosidase staining, cell proliferation, cell cycle analysis, and measurement of reactive oxygen species levels, to investigate NAR's impact on IL-1β-induced senescence and degeneration of NPCs. Our study revealed that Insulin-like growth factor binding protein 3 (IGFBP3) was the only common target. IGFBP3 exhibited significant differences between the IDD and healthy groups and proved to be an effective diagnostic marker for IDD. Molecular docking confirmed the binding between NAR and IGFBP3. In vitro experiments, we observed that Igfbp3 expression increased in the senescence and degeneration groups. Igfbp3 knockdown and NAR attenuated IL-1β-induced senescence and degenerative phenotypes in NPCs. In contrast, the effect of NAR was attenuated by recombinant IGFBP3 protein. In conclusion, our findings suggest that NAR plays a preventive and therapeutic role in IDD, likely achieved through the inhibition of Igfbp3 expression.

The Degree of Cervical Intervertebral Disc Degeneration Is Associated With Denser Bone Quality of the Cervical Sub-endplate and Vertebral Body

OBJECTIVE

The relationship between cervical disc degeneration and bone quality of adjacent vertebral body remains controversial. This study aims to investigate the relationship between cervical disc degeneration and bone quality of the adjacent vertebral body and sub-endplate bone with a new MRI-based bone quality score in patients over 50 years with cervical spondylosis.

METHODS

We retrospectively reviewed 479 cervical disc segments from 131 patients. Disc degeneration at levels C3/C4-C6/C7 was graded using T2-weighted MRI. Vertebral body quality (VBQ) score and sub-endplate bone quality (EBQ) score from C3 to C7 were computed from T1-weighted MRI images. Additionally, bone mineral density (BMD) of the cervical vertebrae was measured in 52 patients using a novel phantom-less quantitative computed tomography (PL-QCT) system. The correlation between bone quality score and Pfirrmann grade was analyzed and risk factors for VBQ and EBQ were further evaluated.

RESULTS

Significant differences were found in cranial VBQ among different Pfirrmann grades, with a score of 2.55 ± 0.54 for Grade 5 discs, which was lower compared to Grades 4 (2.70 ± 0.56) (p < 0.05) and 3 (2.81 ± 0.58) (p < 0.01). Caudal VBQ for Grade 5 discs (2.43 ± 0.52) was also significantly lower than for Grade 3 discs (2.66 ± 0.54) (p < 0.01). EBQ scores decreased with increasing Pfirrmann grades. Negative correlations were observed between both cranial and caudal VBQ and EBQ scores and Pfirrmann grades. Grades 4 and 5 discs were identified as independent risk factors for decreased caudal VBQ and EBQ, whereas only Grade 5 was a significant risk factor for decreased cranial EBQ. Additionally, a moderate correlation (0.4 < R < 0.6, p < 0.05) was noted between vertebral body BMD and VBQ at each cervical level.

CONCLUSION

In individuals over 50 years with cervical spondylosis, the severity of disc degeneration was closely correlated with denser bone quality in both the caudal vertebral body and sub-endplate, as measured by VBQ and EBQ scores. These findings suggest that worsening disc degeneration is associated with increased bone density in specific areas of the cervical spine.

Restoration of physiologic loading after engineered disc implantation mitigates immobilization-induced facet joint and paraspinal muscle degeneration

Intervertebral disc degeneration is commonly associated with back and neck pain, and standard surgical treatments do not restore spine function. Replacement of the degenerative disc with a living, tissue-engineered construct has the potential to restore normal structure and function to the spine. Toward this goal, our group developed endplate-modified disc-like angle-ply structures (eDAPS) that recapitulate the native structure and function of the disc. While our initial large animal studies utilized rigid internal fixation of the eDAPS implanted level to ensure retention of the eDAPS, chronic immobilization does not restore full function and is detrimental to the spinal motion segment. The purpose of this study was to utilize a goat cervical disc replacement model coupled with finite element modeling of goat cervical motion segments to investigate the effects of remobilization (removal of fixation) on the eDAPS, the facet joints and the adjacent paraspinal muscle. Our results demonstrated that chronic immobilization caused notable degeneration of the facet joints and paraspinal muscles adjacent to eDAPS implants. Remobilization improved eDAPS composition and integration and mitigated, but did not fully reverse, facet joint osteoarthritis and paraspinal muscle atrophy and fibrosis. Finite element modeling revealed that these changes were likely due to reduced range of motion and reduced facet loading, highlighting the importance of maintaining normal spine biomechanical function with any tissue engineered disc replacement. STATEMENT OF SIGNIFICANCE: Back and neck pain are ubiquitous in modern society, and the gold standard surgical treatment of spinal fusion limits patient function. This study advances our understanding of the response of the spinal motion segment to tissue engineered disc replacement with provisional fixation in a large animal model, further advancing the clinical translation of this technology.

[Prospects and modern possibilities of non-surgical treatment of intervertebral hernias with neurological manifestations. (Literature review)]

The problem of non-specific pain in the spinal area is important today in society due to a number of reasons, including features of the modern human's lifestyle, tendency to increase in life expectancy and «aging» of population. There is a continuing debate about the sources of this pain and reasonableness of search for them. There is no doubt that discogenic pain prevails over other probable sources of pain in the spinal area and intervertebral hernias play the primary role here. Patients can immediately look for a solution to the problem by a neurosurgeon at the time of «intervertebral disc herniation» diagnosis establishment and in the presence of a pronounced reflex or radicular pain syndrome. It is the «intervertebral disc herniation» wording which often leads patients to a neurosurgeon. There are many methods of intervertebral hernias conservative treatment. This article is focused on the technology of spinal traction therapy, which has a scientific evidence base, including in the question of natural reduction of intervertebral hernias' dimensions. Cyclic local traction therapy is the latest and realizing all important principles of tractive impact on the spine method.

Irisin in degenerative musculoskeletal diseases: Functions in system and potential in therapy

Degenerative musculoskeletal diseases are a class of diseases related to the gradual structural and functional deterioration of muscles, joints, and bones, including osteoarthritis (OA), osteoporosis (OP), sarcopenia (SP), and intervertebral disc degeneration (IDD). As the proportion of aging people around the world increases, degenerative musculoskeletal diseases not only have a multifaceted impact on patients, but also impose a huge burden on the medical industry in various countries. Therefore, it is crucial to find key regulatory factors and potential therapeutic targets. Recent studies have shown that irisin plays an important role in degenerative musculoskeletal diseases, suggesting that it may become a key molecule in the prevention and treatment of degenerative diseases of the musculoskeletal system. Therefore, this review provides a comprehensive description of the release and basic functions of irisin, and summarizes the role of irisin in OA, OP, SP, and IDD from a cellular and tissue perspective, providing comprehensive basis for clinical application. In addition, we summarized the many roles of irisin as a key information molecule in bone-muscle-adipose crosstalk and a regulatory molecule involved in inflammation, senescence, and cell death, and proposed the interesting possibility of irisin in degenerative musculoskeletal diseases.

Role of oxidative stress in mitochondrial dysfunction and their implications in intervertebral disc degeneration: Mechanisms and therapeutic strategies

Background

Intervertebral disc degeneration (IVDD) is widely recognized as one of the leading causes of low back pain. Intervertebral disc cells are the main components of the intervertebral disc (IVD), and their functions include synthesizing and secreting collagen and proteoglycans to maintain the structural and functional stability of the IVD. In addition, IVD cells are involved in several physiological processes. They help maintain nutrient metabolism balance in the IVD. They also have antioxidant and anti-inflammatory effects. Because of these roles, IVD cells are crucial in IVDD. When IVD cells are subjected to oxidative stress, mitochondria may become damaged, affecting normal cell function and accelerating degenerative changes. Mitochondria are the energy source of the cell and regulate important intracellular processes. As a key site for redox reactions, excessive oxidative stress and reactive oxygen species can damage mitochondria, leading to inflammation, DNA damage, and apoptosis, thus accelerating disc degeneration.

Aim of review

Describes the core knowledge of IVDD and oxidative stress. Comprehensively examines the complex relationship and potential mechanistic pathways between oxidative stress, mitochondrial dysfunction and IVDD. Highlights potential therapeutic targets and frontier therapeutic concepts. Draws researchers' attention and discussion on the future research of all three.

Key scientific concepts of review

Origin, development and consequences of IVDD, molecular mechanisms of oxidative stress acting on mitochondria, mechanisms of oxidative stress damage to IVD cells, therapeutic potential of targeting mitochondria to alleviate oxidative stress in IVDD.

The translational potential of this article

Targeted therapeutic strategies for oxidative stress and mitochondrial dysfunction are particularly critical in the treatment of IVDD. Using antioxidants and specific mitochondrial therapeutic agents can help reduce symptoms and pain. This approach is expected to significantly improve the quality of life for patients. Individualized therapeutic approaches, on the other hand, are based on an in-depth assessment of the patient's degree of oxidative stress and mitochondrial functional status to develop a targeted treatment plan for more precise and effective IVDD management. Additionally, we suggest preventive measures like customized lifestyle changes and medications. These are based on understanding how IVDD develops. The aim is to slow down the disease and reduce the chances of it coming back. Actively promoting clinical trials and evaluating the safety and efficacy of new therapies helps translate cutting-edge treatment concepts into clinical practice. These measures not only improve patient outcomes and quality of life but also reduce the consumption of healthcare resources and the socio-economic burden, thus having a positive impact on the advancement of the IVDD treatment field.

Bone Mesenchymal Stem Cells Inhibit Oxidative Stress-Induced Pyroptosis in Annulus Fibrosus Cells to Alleviate Intervertebral Disc Degeneration Based on Matric Hydrogels

Intervertebral disc degeneration (IVDD) is the primary cause of low back pain. Stem cell transplantation may be a possible approach to promote IVDD. This study was aimed to investigate the role of bone mesenchymal stem cells (BMSCs) in IVDD and the molecular mechanism. Annulus fibrosus cells (AFCs) were treated with tert-butyl hydroperoxide (TBHP) to induce oxidative stress injury. AFC biological functions were analyzed using a lactate dehydrogenase kit, enzyme-linked immunosorbent assay, flow cytometry, and western blot. The molecular mechanisms of BMSC functions were assessed using quantitative real-time PCR, western blot, immunoprecipitation (IP), co-IP, GST pull-down, and cycloheximide treatment. Furthermore, the impacts of BMSCs in IVDD progression in vivo were evaluated by magnetic resonance imaging (MRI) and H&E analysis. BMSCs inhibited TBHP-induced inflammation and pyroptosis in AFCs. Knockdown of SIRT1 reversed the effects on inflammation and pyroptosis of BMSCs. Moreover, SIRT1 promoted the deacetylation of ASC rather than NLRP3. SIRT1 interacted with ASC to reduce its protein stability, thereby negatively regulating ASC protein levels. In addition, BMSCs alleviated LPS-induced IVDD based on matrix hydrogels. BMSCs inhibited oxidative stress-induced pyroptosis and inflammation in AFCs, thereby alleviating IVDD, suggesting that BMSCs may contribute to treating intervertebral disc generation.

From structure to therapy: the critical influence of cartilaginous endplates and microvascular network on intervertebral disc degeneration

The intervertebral disc (IVD) is the largest avascular structure in the human body. The cartilaginous endplate (CEP) is a layer of translucent cartilage located at the upper and lower edges of the vertebral bodies. On one hand, CEPs endure pressure from within the IVD and the tensile and shear forces of the annulus fibrosus, promoting uniform distribution of compressive loads on the vertebral bodies. On the other hand, microvascular diffusion channels within the CEP serve as the primary routes for nutrient supply to the IVD and the transport of metabolic waste. Degenerated CEP, characterized by increased stiffness, decreased permeability, and reduced water content, impairs substance transport and mechanical response within the IVD, ultimately leading to intervertebral disc degeneration (IDD). Insufficient nutrition of the IVD has long been considered the initiating factor of IDD, with CEP degeneration regarded as an early contributing factor. Additionally, CEP degeneration is frequently accompanied by Modic changes, which are common manifestations in the progression of IDD. Therefore, this paper comprehensively reviews the structure and physiological functions of CEP and its role in the cascade of IDD, exploring the intrinsic relationship between CEP degeneration and Modic changes from various perspectives. Furthermore, we summarize recent potential therapeutic approaches targeting CEP to delay IDD, offering new insights into the pathological mechanisms and regenerative repair strategies for IDD.

Ephrin B2 (EFNB2) potentially protects against intervertebral disc degeneration through inhibiting nucleus pulposus cell apoptosis

Nucleus pulposus (NP) cell apoptosis is a significant indication of accelerated intervertebral disc degeneration; however, the precise mechanism is unelucidated as of yet. Ephrin B2 (EFNB2), the only gene down-regulated in the three degraded intervertebral disc tissue microarray groups (GSE70362, GSE147383 and GSE56081), was screened for examination in this study. Subsequently, EFNB2 was verified to be down-regulated in degraded NP tissue samples. Interleukin-1 (IL-1β) treatment of NP cells to simulate the IDD environment indicated that IL-1β treatment decreased EFNB2 expression. In degenerative NP cells stimulated by IL-1β, EFNB2 knockdown significantly increased the rate of apoptosis as well as the apoptosis-related molecules cleaved-caspase-3 and the Bax to Bcl-2 ratio. EFNB2 was found to promote AKT, PI3K, and mTOR phosphorylation; the PI3K/AKT signaling role was investigated using the PI3K inhibitor LY294002. EFNB2 overexpression significantly increased PI3K/AKT pathway activity in IL-1β-stimulated NP cells than the normal control. Moreover, EFNB2 partially alleviated NP cell apoptosis induced by IL-1β, reduced the cleaved-cas3 level, and decreased the Bax/Bcl-2 ratio after the addition of the inhibitor LY294002. Additionally, EFNB2 overexpression inhibited the ERK1/2 phosphorylation; the effects of EFNB2 overexpression on ERK1/2 phosphorylation, degenerative NP cell viability, and cell apoptosis were partially reversed by ERK signaling activator Ceramide C6. EFNB2 comprehensively inhibited the apoptosis of NP cells by activating the PI3K/AKT signaling and inhibiting the ERK signaling, obviating the exacerbation of IDD. EFNB2 could be a potential target to protect against degenerative disc changes.

Ginsenoside Rg1 relieves rat intervertebral disc degeneration and inhibits IL-1β-induced nucleus pulposus cell apoptosis and inflammation via NF-κB signaling pathway

The study aimed to investigate the effect of ginsenoside Rg1 on intervertebral disc degeneration (IVDD) in rats and IL-1β-induced nucleus pulposus (NP) cells, and explore its underlying mechanism. Forty IVDD rat models were divided into the IVDD group, low-dose (L-Rg1) group (intraperitoneal injection of 20 mg/kg/d ginsenoside Rg1), medium-dose (M-Rg1) group (intraperitoneal injection of 40 mg/kg/d ginsenoside Rg1), and high-dose (H-Rg1) group (intraperitoneal injection of 80 mg/kg/d ginsenoside Rg1). The pathological change was observed by HE and safranin O-fast green staining. The expression of IL-1β, IL-6, TNF-α, MMP3, aggrecan, and collagen II was detected. The expression of NF-κB p65 in IVD tissues was detected. Rat NP cells were induced by IL-1β to simulate IVDD environment and divided into the control group, IL-1β group, and 20, 50, and 100 µmol/L Rg1 groups. The cell proliferation activity, the apoptosis, and the expression of IL-6, TNF-α, MMP3, aggrecan, collagen II, and NF-κB pathway-related protein were detected. In IVDD rats, ginsenoside Rg1 improved the pathology of IVD tissues; suppressed the expression of IL-1β, IL-6, TNF-α, aggrecan, and collagen II; and inhibited the expression of p-p65/p65 and nuclear translocation of p65, to alleviate the IVDD progression. In the IL-1β-induced NP cells, ginsenoside Rg1 also improved the cell proliferation and inhibited the apoptosis and the expression of IL-6, TNF-α, aggrecan, collagen II, p-p65/p65, and IκK in a dose-dependent manner. Ginsenoside Rg1 alleviated IVDD in rats and inhibited apoptosis, inflammatory response, and ECM degradation in IL-1β-induced NP cells. And Rg1 may exert its effect via inhibiting the activation of NF-κB signaling pathway.

[Sanogenetic mechanisms of cyclic local traction therapy in the treatment of neurological manifestations of degenerative diseases in the spine. (Literature review)]

New information on the results of scientific research may change the understanding of the etiology and pathogenesis of diseases, which makes adjustments in treatment approaches. Cyclic local traction therapywas created in USA by the group of scientists for NASA (Axiom Worldwide, Tampa, FL) and approved by FDA in 2003. The year 2023 is the 20th anniversary of its successful application in practical medicine. Evaluating the effectiveness of the method, it has been shown that after undergoing treatment in patients with chronic back pain, the height of the intervertebral discs increases, pain syndrome and frequency of taking pain medications decreases, daily activity and duration of walking without pain increases. It is assumed that the treatment effect was achieved due to the «vacuum» effect, which could contribute to the regeneration of the intervertebral disc. It is also known about the possibility of intervertebral disc herniation reduction after a course of traction therapy and it was believed that this was ensured by «retraction» of the hernia back into the intervertebral space under the influence of the longitudinal ligament. However, fundamental studies of the past century and the present indicate the presence of other mechanisms affecting the structures of the vertebral motor segment, especially the processes occurring inside the intervertebral disc and contributing to the regression of the intervertebral disc herniation.

Mechanical crosstalk between the intervertebral disc, facet joints, and vertebral endplate following acute disc injury in a rabbit model

Background

Vertebral endplate sclerosis and facet osteoarthritis have been documented in animals and humans. However, it is unclear how these adjacent pathologies engage in crosstalk with the intervertebral disc. This study sought to elucidate this crosstalk by assessing each compartment individually in response to acute disc injury.

Methods

Eleven New Zealand White rabbits underwent annular disc puncture using a 16G or 21G needle. At 4 and 10 weeks, individual compartments of the motion segment were analyzed. Discs underwent T 1 relaxation mapping with MRI contrast agent gadodiamide as well T 2 mapping. Both discs and facets underwent mechanical testing via vertebra-disc-vertebra tension-compression creep testing and indentation testing, respectively. Endplate bone density was quantified via μCT. Discs and facets were sectioned and stained for histology scoring.

Results

Intervertebral discs became more degenerative with increasing needle diameter and time post-puncture. Bone density also increased in endplates adjacent to both 21G and 16G punctured discs leading to reduced gadodiamide transport at 10 weeks. The facet joints, however, did not follow this same trend. Facets adjacent to 16G punctured discs were less degenerative than facets adjacent to 21G punctured discs at 10 weeks. 16G facets were more degenerative at 4 weeks than at 10, suggesting the cartilage had recovered. The formation of severe disc osteophytes in 16G punctured discs between 4 and 10 weeks likely offloaded the facet cartilage, leading to the recovery observed.

Conclusions

Overall, this study supports that degeneration spans the whole spinal motion segment following disc injury. Vertebral endplate thickening occurred in response to disc injury, which limited the diffusion of small molecules into the disc. This work also suggests that altered disc mechanics can induce facet degeneration, and that extreme bony remodeling adjacent to the disc may promote facet cartilage recovery through offloading of the articular cartilage.

Emodin ameliorates matrix degradation and apoptosis in nucleus pulposus cells and attenuates intervertebral disc degeneration through LRP1 in vitro and in vivo

Low back pain (LBP) is the leading cause of disability worldwide, with a strong correlation to intervertebral disc degeneration (IDD). Inflammation-induced extracellular matrix (ECM) degradation plays a major role in IDD's progression. Emodin, known for its anti-inflammatory effects and ability to inhibit ECM degradation in osteoarthritis, but its role in IDD is unclear. Our study aimed to explore emodin's role and mechanisms on IDD both in vivo and in vitro. We discovered that emodin positively regulated anabolic markers (COL2A1, aggrecan) and negatively impacted catabolic markers (MMP3, MMP13) in nucleus pulposus cells, while also inhibiting cell apoptosis under inflammation environment. We revealed that emodin inhibits inflammation-induced NF-ĸB activation by suppressing the degradation of LRP1 via the proteasome pathway. Additionally, LRP1 was validated as essential to emodin's regulation of ECM metabolism and apoptosis, both in vitro and in vivo. Ultimately, we demonstrated that emodin effectively alleviates IDD in a rat model. Our findings uncover the novel pathway of emodin inhibiting ECM degradation and apoptosis through the inhibition of NF-κB via LRP1, thus alleviating IDD. This study not only broadens our understanding of emodin's role and mechanism in IDD treatment but also guides future therapeutic interventions.

Injectable kaempferol-loaded fibrin glue regulates the metabolic balance and inhibits inflammation in intervertebral disc degeneration

To construct an injectable fibrin glue system loaded with kaempferol (FG@F) to improve the bioavailability of kaempferol and observe its efficacy in the treatment of intervertebral disc degeneration (IVDD). Kaempferol-loaded fibrin glue was first synthesized in advance. Subsequently, the materials were characterized by various experimental methods. Then, nucleus pulposus cells (NPCs) were stimulated with lipopolysaccharide (LPS) to establish a degenerative cell model, and the corresponding intervention treatment was conducted to observe the effect in vitro. Finally, the tail disc of rats was punctured to establish a model of IVDD, and the therapeutic effect of the material in vivo was observed after intervertebral disc injection. The FG@F system has good injectability, sustained release and biocompatibility. This treatment reduced the inflammatory response associated with IVDD and regulated matrix synthesis and degradation. Animal experimental results showed that the FG@F system can effectively improve needle puncture-induced IVDD in rats. The FG@F system has better efficacy than kaempferol or FG alone due to its slow release and mechanical properties. The drug delivery and biotherapy platform based on this functional system might also serve as an alternative therapy for IVDD.

Exploring the Interplay of Muscular Endurance, Functional Balance, and Limits of Stability: A Comparative Study in Individuals with Lumbar Spondylosis Using a Computerized Stabilometric Force Platform

Lumbar spondylosis, characterized by degenerative changes in the lumbar spine, often leads to pain, reduced spinal stability, and musculoskeletal dysfunction. Understanding the impact of lumbar spondylosis on musculoskeletal function, particularly lumbar extensor endurance, functional balance, and limits of stability, is crucial for improving the management and well-being of affected individuals. This study aimed to assess lumbar extensor endurance, functional balance, and limits of stability in individuals with lumbar spondylosis compared to age-matched healthy individuals and explore the correlations among these parameters within the lumbar spondylosis group. The lumbar spondylosis group consisted of 60 individuals initially screened by an orthopedician and referred to physical therapy. Age-matched healthy controls (n = 60) were recruited. Inclusion criteria encompassed adults aged 45-70 years for both groups. Lumbar extensor endurance was assessed using the Sorensen test, functional balance with the Berg Balance Scale, and limits of stability using a computerized stabilometric force platform. Lumbar extensor endurance was significantly lower in individuals with lumbar spondylosis compared to healthy controls (23.06 s vs. 52.45 s, p < 0.001). Functional balance, as assessed by the Berg Balance Scale, demonstrated a significant decrement in the lumbar spondylosis group (48.36 vs. 53.34, p < 0.001). Additionally, limits of stability variables, under both eyes-open and eyes-closed conditions, exhibited marked impairments in the lumbar spondylosis group (p < 0.001 for all variables). Within the lumbar spondylosis group, lumbar extensor endurance exhibited significant positive correlations with functional balance (0.46, p < 0.001) and negative correlations with limits of stability variables (r ranging from -0.38 to -0.49, p < 0.01 for all variables). This study underscores the significance of addressing lumbar extensor endurance, functional balance, and stability impairments in the comprehensive management of lumbar spondylosis.

Digoxin protects against intervertebral disc degeneration via TNF/NF-κB and LRP4 signaling

Background

Intervertebral disc degeneration (IVDD) is a leading cause of low back pain (LBP). The pathological process of IVDD is associated with inflammatory reactions and extracellular matrix (ECM) disorders. Digoxin is widely used for treating heart failure, and it has been reported to have anti-inflammatory effects.

Objective

This study is to investigate the role of digoxin in the pathogenesis of intervertebral disc degeneration as well as the involved molecular mechanism, particularly the potential target protein.

Methods

We exploited a rat needle model to investigate digoxin's role in intervertebral disc degeneration in vivo. Safranin O staining was used to measure cartilaginous tissue in the intervertebral disc. The morphological changes of intervertebral discs in animal models were determined by Hematoxylin-Eosin (H&E) staining and the pathological score. Primary nucleus pulposus cells (NP cells) from intervertebral discs of patients and murine were used in the present study. Western-Blotting assay, Real-time PCR assay, immunofluorescence staining, and immunochemistry were used to detect the role of digoxin in anti-TNF-α-induced inflammatory effects in vitro. Transfection of siRNA was used to regulate low-density lipoprotein receptor-related protein 4 (LRP4) expression in NP cells to investigate the potential protein target of digoxin.

Results

Digoxin protected against intervertebral disc degeneration in rat needle models. Digoxin was found to exert its disc-protective effects through at least three different pathways by a) suppressing TNF-α-induced inflammation, b) attenuating ECM destruction, c) significantly promoting ECM anabolism. Additionally, LRP4 was found to be the downstream molecule of digoxin in NP cells for anti-inflammation and regulation of ECM metabolism. The knockdown of LRP4 downregulated the protective effect of digoxin in NP cells.

Conclusion

These findings suggest that digoxin may be a potential therapeutic agent for intervertebral disc degeneration through anti-catabolism and pro-anabolism. Digoxin might also work as an alternative for other inflammation-related diseases.

Contribution of immune cells to intervertebral disc degeneration and the potential of immunotherapy

Substantial evidence supports that chronic low back pain is associated with intervertebral disc degeneration (IDD), which is accompanied by decreased cell activity and matrix degradation. The role of immune cells, especially macrophages, in a variety of diseases has been extensively studied; therefore, their role in IDD has naturally attracted widespread scholarly interest. The IVD is considered to be an immunologically-privileged site given the presence of physical and biological barriers that include an avascular microenvironment, a high proteoglycan concentration, high physical pressure, the presence of apoptosis inducers such as Fas ligand, and the presence of notochordal cells. However, during IDD, immune cells with distinct characteristics appear in the IVD. Some of these immune cells release factors that promote the inflammatory response and angiogenesis in the disc and are, therefore, important drivers of IDD. Although some studies have elucidated the role of immune cells, no specific strategies related to systemic immunotherapy have been proposed. Herein, we summarize current knowledge of the presence and role of immune cells in IDD and consider that immunotherapy targeting immune cells may be a novel strategy for alleviating IDD symptoms.

Sustained release of basic fibroblast growth factor in micro/nanofibrous scaffolds promotes annulus fibrosus regeneration

Tissue engineering has promising applications in the treatment of intervertebral disc degeneration (IDD). The annulus fibrosus (AF) is critical for maintaining the physiological function of the intervertebral disc (IVD), but the lack of vessels and nutrition in AF makes it difficult to repair. In this study, we used hyaluronan (HA) micro-sol electrospinning and collagen type I (Col-I) self-assembly techniques to fabricate layered biomimetic micro/nanofibrous scaffolds, which released basic fibroblast growth factor (bFGF) to promote AF repair and regeneration after discectomy and endoscopic transforaminal discectomy. The bFGF enveloped in the core of the poly-L-lactic-acid (PLLA) core-shell structure was released in a sustained manner and promoted the adhesion and proliferation of AF cells (AFCs). Col-I could self-assemble on the shell of the PLLA core-shell scaffold to mimic the extracellular matrix (ECM) microenvironment, providing structural and biochemical cues for the regeneration of AF tissue. The in vivo studies showed that the micro/nanofibrous scaffolds promoted the repair of AF defects by simulating the microstructure of native AF tissue and inducing endogenous regeneration mechanism. Taken together, the biomimetic micro/nanofibrous scaffolds have clinical potential for the treatment of AF defects caused by IDD. STATEMENT OF SIGNIFICANCE: The annulus fibrosus (AF) is essential for the intervertebral disc (IVD) physiological function, yet it lacks vascularity and nutrition, making repair difficult. Micro-sol electrospinning technology and collagen type I (Col-I) self-assembly technique were combined in this study to create a layered biomimetic micro/nanofibrous scaffold that releases basic fibroblast growth factor (bFGF) to promote AF repair and regeneration. Col-I could mimic the extracellular matrix (ECM) microenvironment, in vivo, offering structural and biochemical cues for AF tissue regeneration. This research indicates that micro/nanofibrous scaffolds have clinical potential for treating AF deficits induced by IDD.

Modic changes as seen on MRI are associated with nonspecific chronic lower back pain and disability

BACKGROUND

Estimating the contribution of endplate oedema known as Modic changes to lower back pain (LBP) has been the subject of multiple observational studies and reviews, some of which conclude that the evidence for an association of Modic change with LBP is uncertain while others demonstrate a clear link. The clinical trials demonstrating the benefit of basivertebral nerve ablation, a therapeutic intervention, in a tightly defined homogenous patient group with chronic LBP and Modic changes type 1 or type 2, provides further evidence for the contribution of Modic changes to LBP and shows that in these subjects, nerve ablation substantially reduces pain and disability. These interventional studies provide direct evidence that Modic changes can be associated with lower back pain and disability. This review set out to explore why the literature to date has been conflicting.

METHODS

A narrative, forensic, non-systematic literature review of selected articles to investigate why the published literature investigating the association between Modic imaging changes and chronic low back pain is inconsistent.

RESULTS

This review found that previous systematic reviews and meta-analyses included both heterogeneous study designs and diverse patient syndromes resulting in an inconsistent association between Modic changes and nonspecific chronic lower back pain. Re-analysis of literature data focussing on more homogenous patient populations provides clearer evidence that Modic changes are associated with nonspecific chronic lower back pain and that type 1 Modic changes are more painful than type 2.

CONCLUSIONS

Studies using tightly defined homogenous patient groups may provide the best test for association between MRI-findings and pain and disability. Clinical benefit of basivertebral nerve ablation observed in randomised controlled trials further supports the association between type 1 and type 2 Modic changes with pain and disability.

Evaluation of the concentration of selected elements in serum patients with intervertebral disc degeneration

Quantitative analysis of the trace element content of human intervertebral discs (IVDs) is essential because it can identify specific enzymes or metabolites that may be related to human intervertebral disc degeneration (IVDD). The goal of this study was to assess the concentrations of copper (Cu), iron (Fe), manganese (Mn), lead (Pb), zinc (Zn), sodium (Na), magnesium (Mg), potassium (K), phosphorus (P), and calcium (Ca) in serum samples obtained from patients with IVDD in comparison to healthy volunteers (a control group). The study group consisted of 113 Caucasian patients qualified by a specialist neurosurgeon for microdiscectomy. The control group consisted of 113 healthy volunteers who met the eligibility criteria for blood donors. The examined clinical material was the serum samples obtained from both groups.Based on the quantitative analysis of selected elements, there were statistically significantly (p 0.05) higher concentrations of Cu (1180 μg/L±800 μg/L vs. 1230 μg/L±750 μg/L), Zn (790 μg/L±300 μg/L vs. 850 μg/L±200 μg/L), and Mg (21730 μg/L±4360 μg/L vs. 23820 μg/L±4990 μg/L) in the serum of healthy volunteers compared to those in the study group. In addition, statistically significant changes were not detected in the concentrations of any elements among either sex in either the study or control group or in their body mass index (BMI) values (p > 0.05). In the serum samples from the study group, the strongest relationships were noted between the concentrations of Zn and Pb (r = 0.61), Zn and P (r = 0.69), Zn and Ca (r = 0.84), Zn and Cu (r = 0.83), Mg and Ca (r = 0.74), and Ca and P (r = 0.98).It has been indicated that, above all, the concentrations of Cu, Zn, Ca, and Mg depend on the advancement of radiological changes, according to the Pfirrmann scale. However, no influence on pain intensity was found, depending on the concentration of the assessed elements.The analysis indicates that the determination of serum Cu, Zn, Ca, and Mg concentrations may have diagnostic significance in predicting the onset of lumbosacral IVDD. The predictive evaluation of changes in the concentrations of selected elements in patients with degenerative lumbar IVD lesions appears to be a promising, cost-effective strategy.

Cellular senescence - Molecular mechanisms of intervertebral disc degeneration from an immune perspective

Intervertebral disc degeneration (IVDD) is a frequent and intractable chronic condition in orthopedics that causes enormous discomfort in patients' lives and thoughts, as well as a significant economic burden on society and the nation. As a result, understanding the pathophysiology of IVDD is critical. The pathophysiology of IVDD has been linked to numerous variables, including oxidative stress, apoptosis, matrix metalloproteinases, and inflammatory factors. Cellular senescence has recently attracted a lot of attention in the study of age-related diseases. It has been discovered that IVDD is intimately linked to human senescence, in which nucleus pulposus cell senescence may play a significant role. Previously, our group did a comprehensive and systematic clarification of the pathogenesis of IVDD from an immune perspective and discovered that the fundamental pathogenesis of IVDD is inflammatory upregulation and nucleus pulposus cell death caused by an imbalance in the immune microenvironment. In this review, we will treat nucleus pulposus cell senescence as a novelty point to clarify the pathophysiology of IVDD and further explore the probable relationship between senescence and immunity along with the dysregulation of the immunological microenvironment to propose new therapeutic approaches for IVDD.

pH-Responsive Delivery of H2 through Ammonia Borane-Loaded Hollow Polydopamine for Intervertebral Disc Degeneration Therapy

An imbalance in oxidative and inflammatory regulation is the main contributor to intervertebral disc degeneration (IDD). Hydrogen (H2) therapy is a promising antioxidation and anti-inflammatory approach. However, the key to the treatment is how to maintain the long-term effective H2 concentration in the intervertebral disc (IVD). Therefore, we developed a pH-responsive delivery of H2 through ammonia borane-loaded hollow polydopamine (AB@HPDA) for IDD therapy, which has sufficient capacity to control long-term H2 release in an acid-dependent manner in degenerative IVD. The characterization, toxicity, and pH-responsive H2 release of AB@HPDA was detected in vitro. The metabolization of AB@HPDA in the degenerated IVD was tested by in vivo imaging. The therapeutic effect of AB@HPDA on IDD was tested in vivo by X-ray, MRI, water content of the disc, and histological changes. Nuclear extracellular matrix (ECM) components, oxidative stress, and inflammation were also tested to explore potential therapeutic mechanisms. AB@HPDA has good biocompatibility at concentrations less than 500 μg/mL. The H2 release of AB@HPDA was pH responsive. Therefore, AB@HPDAs can provide efficient hydrogen therapy with controlled H2 release in response to the acidic degenerated IVD microenvironment. The metabolization of AB@HPDA in IVD was slow and lasted up to 11 days. HPDA and AB@HPDA significantly inhibited IDD, as tested by X-ray, MRI, disc water content, and histology (P < 0.05). pH-responsive H2 delivery through AB@HPDAs has the potential to efficiently treat IDD by inhibiting ECM degradation and rebalancing oxidative stress and inflammation in degenerative IVDs.

A systematic morphology study on the effect of high glucose on intervertebral disc endplate degeneration in mice

To explore the relationship between diabetes and intervertebral disc degeneration in mice and the associated underlying mechanism. Four-week-old male Kunming mice were used to model diabetes using a high-fat diet combined with streptozotocin injection. After 6 months, morphological and pathological changes in L4-L6 intervertebral discs were detected by magnetic resonance imaging, micro-CT and histological staining. Immunostaining of CD31, F4/80 and CD16/32 receptors was used to detect vascular invasion and inflammatory infiltration in endplates; the exact changes were then explored by the transmission electron microscopy. The nucleus pulposus of the control and the diabetic group had a clear boundary and regular shape without collapse, while endplate calcification and chondrocyte abnormality in the diabetic group were more obvious. Immunofluorescence confirmed that compared to control, expression levels of CD31 (vascular endothelial marker) and F4/80 (monocyte/macrophage marker) in the diabetic group were significantly increased (P < 0.05), with an elevated number of F4/80 (+)/CD16/32 (+) cells (P < 0.05). The morphology of endplates was observed by transmission electron microscopy, which showed monocytes/macrophage accumulation in the endplate of the diabetic group, accompanied by increased vascular density, collagen fiber distortion and chondrocyte abnormality. In a conclusion, diabetes promotes endplate degeneration with vascular invasion, monocyte/macrophage infiltration and inflammation in mice.

Biomaterials delivery strategies to repair degenerated intervertebral discs by regulating the inflammatory microenvironment

Intervertebral disc degeneration (IVDD) is one of the leading causes of lower back pain. Although IVDD cannot directly cause death, it can cause pain, psychological burdens, and economic burdens to patients. Current conservative treatments for IVDD can relieve pain but cannot reverse the disease. Patients who cannot tolerate pain usually resort to a strategy of surgical resection of the degenerated disc. However, the surgical removal of IVDD can affect the stability of adjacent discs. Furthermore, the probability of the reherniation of the intervertebral disc (IVD) after surgery is as high as 21.2%. Strategies based on tissue engineering to deliver stem cells for the regeneration of nucleus purposes (NP) and annulus fibrosus (AF) have been extensively studied. The developed biomaterials not only locally withstand the pressure of the IVD but also lay the foundation for the survival of stem cells. However, the structure of IVDs does not provide sufficient nutrients for delivered stem cells. The role of immune mechanisms in IVDD has recently become clear. In IVDD, the IVD that was originally in immune privilege prevents the attack of immune cells (mainly effector T cells and macrophages) and aggravates the disease. Immune regulatory and inflammatory factors released by effector T cells, macrophages, and the IVD further aggravate IVDD. Reversing IVDD by regulating the inflammatory microenvironment is a potential approach for the treatment of the disease. However, the biological factors modulating the inflammatory microenvironment easily degrade in vivo. It makes it possible for different biomaterials to modulate the inflammatory microenvironment to repair IVDD. In this review, we have discussed the structures of IVDs and the immune mechanisms underlying IVDD. We have described the immune mechanisms elicited by different biological factors, including tumor necrosis factors, interleukins, transforming growth factors, hypoxia-inducible factors, and reactive oxygen species in IVDs. Finally, we have discussed the biomaterials used to modulate the inflammatory microenvironment to repair IVDD and their development.

Usefulness of Detecting Brain-Derived Neurotrophic Factor in Intervertebral Disc Degeneration of the Lumbosacral Spine

BACKGROUND In determining the etiology of pain of discogenic origin, attention is paid to the role of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF). Considering the potential role of BDNF in the etiology of pain during intervertebral disc degeneration (IVDD), this study aimed to assess changes in the number of BDNF-positive nerve fibers and levels of BDNF in IVDD of the lumbosacral spine in comparison to intervertebral discs (IVDs) of the control group (cadavers). MATERIAL AND METHODS The study group comprised 113 patients with IVDD of the lumbosacral spine. The control group consisted of 81 people (cadavers). We performed hematoxylin-eosin staining to assess IVD structures (degeneration), immunohistochemistry to determine the number of BDNF-positive nerve fibers, and an enzyme-linked immunosorbent assay and western blot to quantify BDNF levels in IVDs. RESULTS Levels of BDNF in the study group were significantly higher than in the control group (17.91±19.58 pg/mg; P<0.05). Furthermore, BDNF levels were significantly higher in the annulus fibrosus compared to the nucleus pulposus of the intervertebral disc (5.50±6.40 pg/mg; P<0.05). Neither the number of BDNF-positive nerves (P=0.359) nor BDNF concentration (P=0.706) were significantly correlated with the degree of perceived pain. The number of BDNF-positive fibers per 1 mm2 was not found to differ significantly according to the radiological degree of degeneration of the lumbosacral spine based on the Pfirrmann scale (P=0.735). CONCLUSIONS The level of BDNF expression may be indicative of IVD degeneration, although it does not predict the degree of this degeneration.

Role of Pyroptosis in Intervertebral Disc Degeneration and Its Therapeutic Implications

Intervertebral disc degeneration (IDD), a progressive and multifactorial pathological process, is predominantly associated with low back pain and permanent disability. Pyroptosis is a type of lytic programmed cell death triggered by the activation of inflammasomes and caspases. Unlike apoptosis, pyroptosis is characterized by the rupture of the plasma membrane and the release of inflammatory mediators, accelerating the destruction of the extracellular matrix (ECM). Recent studies have shown that pyrin domain-containing 3 (NLRP3) inflammasome-mediated pyroptosis in nucleus pulposus (NP) cells is activated in the progression of IDD. Furthermore, targeting pyroptosis in IDD demonstrates the excellent capacity of ECM remodeling and its anti-inflammatory properties, suggesting that pyroptosis is involved in the IDD process. In this review, we briefly summarize the molecular mechanism of pyroptosis and the pathogenesis of IDD. We also focus on the role of pyroptosis in the pathological progress of IDD and its targeted therapeutic application.

Rat tail models for the assessment of injectable nucleus pulposus regeneration strategies

Back pain is a global epidemiological and socioeconomic problem often associated with intervertebral disc degeneration; a condition believed to initiate in the nucleus pulposus (NP). There is considerable interest in developing early therapeutic interventions to target the NP and halt degeneration. Rat caudal models of disc degeneration have demonstrated significant utility in the study of disease progression and its impact on tissue structure, composition, and mechanical performance. One significant advantage of the caudal model is the ease of access and high throughput nature. However, considerable variability exists across the literature in terms of experimental setup and parameters. The objective of this article is to aid researchers in the design and development of caudal puncture models by providing details and insight into the most reported experimental parameters. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were employed to screen the existing literature and 80 manuscripts met the inclusion criteria. Disc geometry, surgical approaches, effect of needle gauge size to induce degeneration, therapeutic volume, outcome measures, and associated limitations are considered and discussed, and a range of recommendations based on different research questions are presented.

Magnetic Resonance Imaging Characteristics Associated with Treatment Success from Basivertebral Nerve Ablation: An Aggregated Cohort Study of Multicenter Prospective Clinical Trials Data

OBJECTIVE

Investigate associations between endplate and motion segment magnetic resonance imaging (MRI) characteristics and treatment outcomes following basivertebral nerve radiofrequency ablation (BVN RFA) in patients with clinically suspected vertebral endplate pain (VEP).

DESIGN

Aggregated cohort study of 296 participants treated with BVN RFA from three prospective clinical trials.

METHODS

Baseline MRI characteristics were analyzed using stepwise logistic regression to identify factors associated with treatment success. Predictive models used three definitions of treatment success: (1) ≥50% low back pain (LBP) visual analog scale (VAS), (2) ≥15-point Oswestry Disability Index (ODI), and (3) ≥50% VAS or ≥15-point ODI improvements at 3-months post-BVN RFA.

RESULTS

The presence of lumbar facet joint fluid (odds ratio [OR] 0.586) reduced the odds of BVN RFA treatment success in individuals with clinically suspected VEP. In patients with a less advanced degenerative disc disease (DDD) profile, a > 50% area of the endplate with bone marrow intensity changes (BMIC) was predictive of treatment success (OR 4.689). Both regressions areas under the curve (AUCs) were under 70%, indicating low predictive value. All other vertebral endplate, intervertebral disc, nerve roots facet joint, spinal segmental alignment, neuroforamina, lateral recesses, and central canal MRI characteristics were not associated with BVN RFA success.

CONCLUSIONS

In patients with vertebrogenic low back pain with Modic changes, the presence of degenerative findings of the anterior and posterior column was not associated with a clinically important impact on BVN RFA treatment success. None of the models demonstrated strong predictive value, indicating that the use of objective imaging biomarkers (Type 1 and/or 2 Modic changes) and a correlating presentation of pain remain the most useful patient selection factors for BVN RFA.

Irisin Ameliorates Intervertebral Disc Degeneration by Activating LATS/YAP/CTGF Signaling

Unbalanced metabolism of an extracellular matrix (ECM) in nucleus pulposus cells (NPCs) is widely acknowledged as the primary cause of intervertebral disc degeneration (IDD). Irisin, a novel myokine, is cleaved from fibronectin type III domain-containing 5 (FNDC5) and has recently been proven to regulate the metabolism of ECM. However, little is known about its potential on NPCs and the development of IDD. Therefore, this study sought to examine the protective effects and molecular mechanism of irisin on IDD in vivo and in vitro. Decreased expression levels of FNDC5 and anabolism markers (COL2A1 and ACAN) but increased levels of catabolism markers (ADAMTS4) were found in degenerative nucleus pulposus (NP) tissues. In a punctured-induced rat IDD model, irisin treatment was found to significantly slow the development of IDD, and in TNF-α-stimulated NPCs, irisin treatment partly reversed the disorder of ECM metabolism. In mechanism, RNA-seq results suggested that irisin treatment affected the Hippo signaling pathway. Further studies revealed that with irisin treatment, the phosphorylation levels of key factors (LATS and YAP) were downregulated, while the expression level of CTGF was upregulated. Moreover, CTGF knockdown partially eliminated the protective effects of irisin on the metabolism of ECM in NPCs, including inhibiting the anabolism and promoting the catabolism. Taken together, this study demonstrated that the expression levels of FNDC5 were decreased in degenerative NP tissues, while irisin treatment promoted the anabolism, inhibited the catabolism of the ECM in NPCs, and delayed the progression of IDD via LATS/YAP/CTGF signaling. These results shed light on the protective actions of irisin on NPCs, leading to the development of a novel therapeutic target for treating IDD.

Circular RNA hsa_circ_0083756 promotes intervertebral disc degeneration by sponging miR-558 and regulating TREM1 expression

Objectives

Intervertebral disc degeneration (IVDD) is a leading cause of low back pain. Circular RNAs (circRNAs) have been demonstrated to exert vital functions in IVDD. However, the role and mechanism of hsa_circ_0083756 in the development of IVDD remain unclear.

Materials and methods

RT‐qPCR was performed to detect expressions of hsa_circ_0083756, miR‐558 and TREM1 in nucleus pulposus (NP) tissues and cells. CCK8 assay, flow cytometry, TUNEL assay, RT‐qPCR and WB were used to clarify the roles of hsa_circ_0083756 in NP cells proliferation and extracellular matrix (ECM) formation. Bioinformatics analyses, dual‐luciferase reporter gene experiment, RNA immunoprecipitation (RIP) assay and FISH assay were performed to predict and verify the targeting relationship between hsa_circ_0083756 and miR‐558, as well as that between miR‐558 and TREM1. Ultimately, the effect of hsa_circ_0083756 on IVDD was tested through anterior disc‐puncture IVDD animal model in rats.

Results

hsa_circ_0083756 was upregulated in degenerative NP tissues and cells. In vitro loss‐of‐function and gain‐of‐function studies suggested that hsa_circ_0083756 knockdown promoted, whereas hsa_circ_0083756 overexpression inhibited NP cells proliferation and ECM formation. Mechanistically, hsa_circ_0083756 acted as a sponge of miR‐558 and subsequently promoted the expression of TREM1. Furthermore, in vivo study indicated that silencing of hsa_circ_0083756 could alleviate IVDD in rats.

Conclusions

hsa_circ_0083756 promoted IVDD via targeting the miR‐558/TREM1 axis, and hsa_circ_0083756 may serve as a potential therapeutic target for the treatment of IVDD.

Advances and Prospects in Biomaterials for Intervertebral Disk Regeneration

Low-back and neck-shoulder pains caused by intervertebral disk degeneration are highly prevalent among middle-aged and elderly people globally. The main therapy method for intervertebral disk degeneration is surgical intervention, including interbody fusion, disk replacement, and diskectomy. However, the stress changes caused by traditional fusion surgery are prone to degeneration of adjacent segments, while non-fusion surgery has problems, such as ossification of artificial intervertebral disks. To overcome these drawbacks, biomaterials that could endogenously regenerate the intervertebral disk and restore the biomechanical function of the intervertebral disk is imperative. Intervertebral disk is a fibrocartilaginous tissue, primarily comprising nucleus pulposus and annulus fibrosus. Nucleus pulposus (NP) contains high water and proteoglycan, and its main function is absorbing compressive forces and dispersing loads from physical activities to other body parts. Annulus fibrosus (AF) is a multilamellar structure that encloses the NP, comprises water and collagen, and supports compressive and shear stress during complex motion. Therefore, different biomaterials and tissue engineering strategies are required for the functional recovery of NP and AF based on their structures and function. Recently, great progress has been achieved on biomaterials for NP and AF made of functional polymers, such as chitosan, collagen, polylactic acid, and polycaprolactone. However, scaffolds regenerating intervertebral disk remain unexplored. Hence, several tissue engineering strategies based on cell transplantation and growth factors have been extensively researched. In this review, we summarized the functional polymers and tissue engineering strategies of NP and AF to endogenously regenerate degenerative intervertebral disk. The perspective and challenges of tissue engineering strategies using functional polymers, cell transplantation, and growth factor for generating degenerative intervertebral disks were also discussed.

The hippo pathway orchestrates cytoskeletal organisation during intervertebral disc degeneration

Yes-associated protein (YAP) activity responded to physical and mechanical cues such as extracellular matrix (ECM), cell density and the mechanical regulation of YAP controlled cellular proliferation and inhibition of apoptotic signals. The intervertebral disc (IVD) comprises a heterogeneous population of cells, including those of the nucleus pulposus (NP) and annulus fibrosus (AF), which are diverse in phenotype, partly due to the different ECM and mechanical loads they experience. How do IVD cells sense microenvironment and what is the relationship between YAP and cytoskeleton in the process of intervertebral disc degeneration (IDD) are not well understood. First, Hippo pathway and cytoskeleton organisation were assessed in the NP and AF of immature (4 weeks), mature (14 weeks), aged (50 weeks), and degenerated (14 weeks, 4 weeks after annulus puncture) IVDs. Second, to assess the effect of ECM composition and cell density on cytoskeleton and YAP levels, we seeded cells at different densities on three types of ECM. In this study, YAP and F-actin activity decreased gradually with age in natural IDD. Hippo signalling was suppressed in the early stages of disc injury, demonstrating the potential for endogenous repair, but this repair did not prevent further disc degeneration. β-tubulin and vimentin filaments provide the cell with its shape and its elastic properties in resisting mechanical forces. The Hippo pathway and cytoskeleton were shown to be regulated by cell density and the ECM composition.