Degenerate intervertebral disc-like pH induces a catabolic mechanoresponse in human nucleus pulposus cells

Stimuli-Responsive Delivery Systems for Intervertebral Disc Degeneration

As a major cause of low back pain, intervertebral disc degeneration is an increasingly prevalent chronic disease worldwide that leads to huge annual financial losses. The intervertebral disc consists of the inner nucleus pulposus, outer annulus fibrosus, and sandwiched cartilage endplates. All these factors collectively participate in maintaining the structure and physiological functions of the disc. During the unavoidable degeneration stage, the degenerated discs are surrounded by a harsh microenvironment characterized by acidic, oxidative, inflammatory, and chaotic cytokine expression. Loss of stem cell markers, imbalance of the extracellular matrix, increase in inflammation, sensory hyperinnervation, and vascularization have been considered as the reasons for the progression of intervertebral disc degeneration. The current treatment approaches include conservative therapy and surgery, both of which have drawbacks. Novel stimuli-responsive delivery systems are more promising future therapeutic options than traditional treatments. By combining bioactive agents with specially designed hydrogels, scaffolds, microspheres, and nanoparticles, novel stimuli-responsive delivery systems can realize the targeted and sustained release of drugs, which can both reduce systematic adverse effects and maximize therapeutic efficacy. Trigger factors are categorized into internal (pH, reactive oxygen species, enzymes, etc.) and external stimuli (photo, ultrasound, magnetic, etc.) based on their intrinsic properties. This review systematically summarizes novel stimuli-responsive delivery systems for intervertebral disc degeneration, shedding new light on intervertebral disc therapy.

Bioenergetic dysfunction in the pathogenesis of intervertebral disc degeneration

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

Multiplex gene editing to promote cell survival using low-pH clustered regularly interspaced short palindromic repeats activation (CRISPRa) gene perturbation

BACKGROUND AIMS

Lower back pain is the leading cause of disability worldwide and is often linked to degenerative disc disease (DDD), the breakdown of intervertebral discs. The majority of treatment options for DDD are palliative, with clinicians prescribing medication or physical therapy to return the patient to work. Cell therapies are promising treatment options with the potential to restore functional physiological tissue and treat the underlying causes of DDD. DDD is characterized by biochemical changes in the microenvironment of the disc, including changes in nutrient levels, hypoxia, and changes in pH. Stem cell therapies are promising therapies to treat DDD, but the acidic environment in a degenerating disc significantly hinders the viability of stem cells, affecting their efficacy. Clustered regularly interspaced short palindromic repeats (CRISPR) systems allow us to engineer cell phenotypes in a well-regulated and controlled manner. Recently, CRISPR gene perturbation screens have assessed fitness, growth and provided a means for specific cell phenotype characterization.

METHODS

In this study, we use a CRISPR-activation (a) gene perturbation screen to identify gene upregulation targets that enhance adipose-derived stem cell survival in acidic culture conditions.

RESULTS

We identified 1213 prospective pro-survival genes and systematically narrowed these down to 20 genes for validation. We further narrowed down our selection to the top five prospective genes using Cell Counting Kit-8 cell viability assays in naïve adipose-derived stem cells and ACAN/Col2 CRISPRa upregulated stem cells. Finally, we examined the extracellular matrix-producing abilities of multiplex ACAN/Col2-pro-survival edited cells in pellet culture.

CONCLUSIONS

Using the results from the CRISPRa screen, we are able to engineer desirable cell phenotypes to improve cell viability for the potential treatment of DDD and other disease states that expose cell therapies to acidic environments, while also providing broader knowledge on genes regulating low-pH cell survival.

The Clinical Efficacy of Autologous Platelet-Rich Plasma Interventional Circulatory Perfusion Combined with Radiofrequency Ablation and Thermocoagulation in the Treatment of Discogenic Low Back Pain

Objective

In this study, we aimed to explore the efficacy of the autologous platelet-rich plasma (PRP) interventional circulatory perfusion combined with radiofrequency ablation and thermocoagulation (RFAT) in the treatment of discogenic low back pain (DLBP).

Methods

From January 2020 to November 2022, 158 patients of the Second Affiliated Hospital of Nanchang University were selected as the study subjects, and 24 patients met the exclusion criteria. The 134 patients who met the inclusion criteria were divided into 65 patients in the control group (3 patients lost to follow-up) and 69 patients in the observation group (5 patients lost to follow-up), so 126 patients were actually completed the study, including 62 patients in the control group and 64 patients in the observation group. The control group responsible disc received RFAT, and an interventional circulatory perfusion was performed; the observation group received RFAT, and an interventional circulatory perfusion was performed, and then autologous PRP 2 ml was injected. Visual Analog Scale (VAS) and Oswestry Disability Index (ODI) were performed before and 4 and 8 weeks after treatment, and the efficacy was evaluated at 4 and 8 weeks after treatment. The changes of lumbar disc MRI before and after treatment were observed.

Results

The differences in the Visual Analog Scale (VAS) scores and the Oswestry Disability Index (ODI) between the observation group and the control group before the treatment were not statistically significant (P > 0.05 in both). However, four weeks and eight weeks after the treatment, the VAS scores and the ODIs were significantly lower in both groups than those before the treatment (P < 0.05 in both). In terms of the therapeutic efficacy, eight weeks after the treatment, the total effective rates in the control group and the observation group were 67.7% and 87.5%, respectively, with the observation group being superior to the control group (P < 0.05).

Conclusion

After RFAT, interventional circulatory perfusion combined with autologous PRP intramedullary injection in the lumbar disc is a safe and effective treatment for DLBP, and it had superior long-term effects in improving the clinical symptoms and patient dysfunction than the RFAT and interventional circulatory perfusion.

Mechanobiology of the Human Intervertebral Disc: Systematic Review of the Literature and Future Perspectives

Low back pain is an extremely common condition with severe consequences. Among its potential specific causes, degenerative disc disease (DDD) is one of the most frequently observed. Mechanobiology is an emerging science studying the interplay between mechanical stimuli and the biological behavior of cells and tissues. The aim of the presented study is to review, with a systematic approach, the existing literature regarding the mechanobiology of the human intervertebral disc (IVD), define the main pathways involved in DDD and identify novel potential therapeutic targets. The review was carried out in accordance with the Preferential Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. Studies were included if they described biological responses of human IVD cells under mechanical stimulation or alterations of mechanical properties of the IVD determined by different gene expression. Fifteen studies were included and showed promising results confirming the mechanobiology of the human IVD as a key element in DDD. The technical advances of the last decade have allowed us to increase our understanding of this topic, enabling us to identify possible therapeutic targets to treat and to prevent DDD. Further research and technological innovations will shed light on the interactions between the mechanics and biology of the human IVD.

High hydrostatic pressure (30 atm) enhances the apoptosis and inhibits the proteoglycan synthesis and extracellular matrix level of human nucleus pulposus cells via promoting the Wnt/β-catenin pathway

Hydrostatic pressure is known to regulate bovine nucleus pulposus cell metabolism, but its mechanism in human nucleus pulposus cells (HNPCs) remains obscure, which attracts our attention and becomes the focus in this study. Specifically, HNPCs were treated with SKL2001 (an agonist in the Wnt/β-catenin pathway) or XAV-939 (an inhibitor of the Wnt/β-catenin pathway), and pressurized under the hydrostatic pressure of 1, 3 and 30 atm. The viability, apoptosis and proteoglycan synthesis of treated HNPC were assessed by CCK-8, flow cytometry and radioisotope incorporation assays. The levels of extracellular matrix, Collagen-II, matrix metalloproteinase 3 (MMP3), Wnt-3a and β-catenin were measured by toluidine blue staining, immunocytochemistry and Western blot. Appropriate hydrostatic stimulation (3 atm) enhanced the viability and proteoglycan synthesis yet inhibited the apoptosis of HNPCs, which also up-regulated extracellular matrix and Collagen-II levels, and down-regulated MMP3, Wnt-3a and β-catenin levels in treated HNPCs. Furthermore, high hydrostatic pressure (30 atm) inhibited the viability and proteoglycan synthesis, and promoted the morphological change and apoptosis of HNPCs, which also down-regulated extracellular matrix and Collagen-II levels and up-regulated MMP3, Wnt-3a and β-catenin levels. Besides, SKL2001 reversed the effects of hydrostatic pressure (3 atm) on inhibiting Wnt-3a, β-catenin, and MMP3 levels and promoting Collagen-II level in HNPC; whereas, XAV-939 reversed the effects of high hydrostatic pressure (30 atm) on promoting MMP3, Wnt-3a, and β-catenin levels and inhibiting Collagen-II level and proteoglycan synthesis of HNPCs. Collectively, high hydrostatic pressure promoted the apoptosis and inhibited the viability of HNPCs via activating the Wnt/β-catenin pathway.

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

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

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

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

Multiscale Regulation of the Intervertebral Disc: Achievements in Experimental, In Silico, and Regenerative Research

Intervertebral disc (IVD) degeneration is a major risk factor of low back pain. It is defined by a progressive loss of the IVD structure and functionality, leading to severe impairments with restricted treatment options due to the highly demanding mechanical exposure of the IVD. Degenerative changes in the IVD usually increase with age but at an accelerated rate in some individuals. To understand the initiation and progression of this disease, it is crucial to identify key top-down and bottom-up regulations' processes, across the cell, tissue, and organ levels, in health and disease. Owing to unremitting investigation of experimental research, the comprehension of detailed cell signaling pathways and their effect on matrix turnover significantly rose. Likewise, in silico research substantially contributed to a holistic understanding of spatiotemporal effects and complex, multifactorial interactions within the IVD. Together with important achievements in the research of biomaterials, manifold promising approaches for regenerative treatment options were presented over the last years. This review provides an integrative analysis of the current knowledge about (1) the multiscale function and regulation of the IVD in health and disease, (2) the possible regenerative strategies, and (3) the in silico models that shall eventually support the development of advanced therapies.

Increased lactic acid content associated with extracellular matrix depletion in a porcine disc degeneration induced by superficial annular lesion

Background

Degenerative intervertebral disc (IVD) disease can cause lower back pain. However, the change of lactic acid content during disc degeneration process still unclear. The objective of this study was to investigate whether the change of the content of lactic acid is associated with depletion of degenerative intervertebral disc extracellular matrix.

Methods

A total of 18 miniature pigs were equally divided into annular lesion surgery (AL) and sham group. The lateral superficial annulus fibrosus (AF) of T12-L4 discs in AL group were penetrated by 3.5 mm trepan with the depth of 3 mm, the same IVD were only exposed without any injury in the sham group. At 4, 8 and 12 weeks after surgery, the degree of intervertebral disc degeneration was evaluated by magnetic resonance, histological and biochemical analysis.

Results

No obvious degeneration was found in sham group. However, disc degeneration was found and gradually worsened in AL group after surgery. Histological analysis showed that the AF was rupture and disorder, the number of cells in nucleus pulposus (NP) was decreased in AL group. Compared with the sham group, the extent of type II collagen (Col-II) and aggrecan in NP tissue was dramatically decreased in AL group, consistent with the results of Col -II immunohistochemistry staining and quantitative reverse transcription polymerase chain reaction (qRT-PCR). Besides, the gene expression of matrix metallopeptidase 3 and 13 also continuous increased in AL group. The amount of lactic acid and nerve growth factor in NP tissue was gradually increased after operation in AL group.

Conclusions

The content of lactic acid gradually increased after annular lesion, associated with the damage of AF structural and the decrease of Col -II and aggrecan in NP tissue, which leading to the disc degeneration. Depletion of extracellular matrix is consistent with lactic acid accumulation inside of IVD.