Intervertebral disc tissue engineering: A brief review

Exosomal U2AF2 derived from human bone marrow mesenchymal stem cells attenuates the intervertebral disc degeneration through circ_0036763/miR-583/ACAN axis

Intervertebral disc degeneration (IDD) is one of the major leading causes of back pain affecting the patient's quality of life. However, the roles of circular RNA (circRNA) in IDD remains unclear. This study aimed to explore the function and underlying mechanism of circ_0036763 in IDD. In this study, expressions of circ_0036763, U2 small nuclear RNA auxiliary factor 2 (U2AF2), miR-583 and aggrecan (ACAN) in primary human nucleus pulposus cells (HNPCs) derived from IDD patients and healthy controls were detected by quantitative real-time reverse transcription-PCR (qRT-PCR) or Western blot (WB). The relationship between pre-circ_0036763 and U2AF2, circ_0036763 and miR-583, miR-583 and ACAN mRNA was determined by bioinformatic analysis, miRNA pull down or RNA immunoprecipitation (RIP) assay. The expressions of Collagen I and Collagen II were evaluated by WB. Co-culture of bone marrow mesenchymal stem cells (bMSCs) or bMSCs-derived exosomes and HNPCs were performed to identify the effect of U2AF2 on the mature of circ_0036763 and ACAN. Results indicated that circ_0036763, U2AF2 and ACAN were downregulated while miR-583 was upregulated in HNPCs derived from IDD patients compared with that in normal HNPCs. Besides, overexpression of circ_0036763 elevated the expressions of ACAN and Collagen II whereas reduced Collagen I expression in HNPCs. Moreover, U2AF2 promoted the mature of circ_0036763, and circ_0036763 positively regulated ACAN by directly sponging miR-583. Furthermore, exosomal U2AF2 derived from bMSCs could increase U2AF2 levels in HNPCs and subsequently regulate the expression of ACAN by circ_0036763/miR-583 axis. In summary, circ_0036763 modified by exosomal U2AF2 derived from bMSCs alleviated IDD through regulating miR-583/ACAN axis in HNPCs. Thus, this study might provide novel therapeutic targets for IDD.

Reviving Intervertebral Discs: Treating Degeneration Using Advanced Delivery Systems

Intervertebral disc degeneration (IVDD) is commonly associated with many spinal problems, such as low back pain, and significantly impacts a patient's quality of life. However, current treatments for IVDD, which include conservative and surgical methods, are limited in their ability to fully address degeneration. To combat IVDD, delivery-system-based therapy has received extensive attention from researchers. These delivery systems can effectively deliver therapeutic agents for IVDD, overcoming the limitations of these agents, reducing leakage and increasing local concentration to inhibit IVDD or promote intervertebral disc (IVD) regeneration. This review first briefly introduces the structure and function of the IVD, and the related pathophysiology of IVDD. Subsequently, the roles of drug-based and bioactive-substance-based delivery systems in IVDD are highlighted. The former includes natural source drugs, nonsteroidal anti-inflammatory drugs, steroid medications, and other small molecular drugs. The latter includes chemokines, growth factors, interleukin, and platelet-rich plasma. Additionally, gene-based and cell-based delivery systems are briefly involved. Finally, the limitations and future development of the combination of therapeutic agents and delivery systems in the treatment of IVDD are discussed, providing insights for future research.

Intervertebral disc degeneration-Current therapeutic options and challenges

Degeneration of the intervertebral disc (IVD) is a normal part of aging. Due to the spine's declining function and the development of pain, it may affect one's physical health, mental health, and socioeconomic status. Most of the intervertebral disc degeneration (IVDD) therapies today focus on the symptoms of low back pain rather than the underlying etiology or mechanical function of the disc. The deteriorated disc is typically not restored by conservative or surgical therapies that largely focus on correcting symptoms and structural abnormalities. To enhance the clinical outcome and the quality of life of a patient, several therapeutic modalities have been created. In this review, we discuss genetic and environmental causes of IVDD and describe promising modern endogenous and exogenous therapeutic approaches including their applicability and relevance to the degeneration process.

The role of biomechanical factors in models of intervertebral disc degeneration across multiple length scales

Low back pain is the leading cause of disability, producing a substantial socio-economic burden on healthcare systems worldwide. Intervertebral disc (IVD) degeneration is a primary cause of lower back pain, and while regenerative therapies aimed at full functional recovery of the disc have been developed in recent years, no commercially available, approved devices or therapies for the regeneration of the IVD currently exist. In the development of these new approaches, numerous models for mechanical stimulation and preclinical assessment, including in vitro cell studies using microfluidics, ex vivo organ studies coupled with bioreactors and mechanical testing rigs, and in vivo testing in a variety of large and small animals, have emerged. These approaches have provided different capabilities, certainly improving the preclinical evaluation of these regenerative therapies, but challenges within the research environment, and compromises relating to non-representative mechanical stimulation and unrealistic test conditions, remain to be resolved. In this review, insights into the ideal characteristics of a disc model for the testing of IVD regenerative approaches are first assessed. Key learnings from in vivo, ex vivo, and in vitro IVD models under mechanical loading stimulation to date are presented alongside the merits and limitations of each model based on the physiological resemblance to the human IVD environment (biological and mechanical) as well as the possible feedback and output measurements for each approach. When moving from simplified in vitro models to ex vivo and in vivo approaches, the complexity increases resulting in less controllable models but providing a better representation of the physiological environment. Although cost, time, and ethical constraints are dependent on each approach, they escalate with the model complexity. These constraints are discussed and weighted as part of the characteristics of each model.

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.

Endplate role in the degenerative disc disease: A brief review

The degenerative disease of the intervertebral disc is nowadays an important health problem, which has still not been understood and solved adequately. The vertebral endplate is regarded as one of the vital elements in the structure of the intervertebral disc. Its constituent cells, the chondrocytes in the endplate, may also be involved in the process of the intervertebral disc degeneration and their role is central both under physiological and pathological conditions. They main functions include a role in homeostasis of the extracellular environment of the intervertebral disc, metabolic support and nutrition of the discal nucleus and annulus beneath and the preservation of the extracellular matrix. Therefore, it is understandable that the cells in the endplate have been in the centre of research from several viewpoints, such as development, degeneration and growth, reparation and remodelling, as well as treatment strategies. In this article, we briefly review the importance of vertebral endplate, which are often overlooked, in the intervertebral disc degeneration.

New strategies for the treatment of intervertebral disc degeneration: cell, exosome, gene, and tissue engineering

Low back pain (LBP) caused by intervertebral disc (IVD) generation (IVDD) has always been an important problem that cannot be ignored. Traditional therapies have many deep-rooted and intractable complications that promote their treatment mode transfer to new therapies. This article mainly summarizes the shortcomings of traditional treatment methods and analyzes the research status and future development direction of IVDD treatment. We outlined the most promising IVDD therapies, including cell, exosome, gene, and tissue engineering therapy, especially tissue engineering therapy, which runs through the whole process of other therapies. In addition, the article focuses on the cellular, animal, and preclinical challenges faced by each therapeutic approach, as well as their respective advantages and disadvantages, to provide better ideas for relieving the IVDD patients' pain through new treatment methods.

Design of a flexing organ-chip to model in situ loading of the intervertebral disc

The leading cause of disability of all ages worldwide is severe lower back pain. To address this untreated epidemic, further investigation is needed into the leading cause of back pain, intervertebral disc degeneration. In particular, microphysiological systems modeling critical tissues in a degenerative disc, like the annulus fibrosus (AF), are needed to investigate the effects of complex multiaxial strains on AF cells. By replicating these mechanobiological effects unique to the AF that are not yet understood, we can advance therapies for early-stage degeneration at the cellular level. To this end, we designed, fabricated, and collected proof-of-concept data for a novel microphysiological device called the flexing annulus-on-a-chip (AoC). We used computational models and experimental measurements to characterize the device's ability to mimic complex physiologically relevant strains. As a result, these strains proved to be controllable, multi-directional, and uniformly distributed with magnitudes ranging from - 10 % to 12% in the axial, radial, and circumferential directions, which differ greatly from applied strains possible in uniaxial devices. Furthermore, after withstanding accelerated life testing (66 K cycles of 10% strain) and maintaining 2000 bovine AF cells without loading for more than three weeks the AoC proved capable of long-term cell culture. Additionally, after strain (3.5% strain for 75 cycles at 0.5 Hz) was applied to a monolayer of AF cells in the AoC, a population remained adhered to the channel with spread morphology. The AoC can also be tailored for other annular structures in the body such as cardiovascular vessels, lymphatic vessels, and the cervix.

Fabrication and Evaluation of Gellan Gum/Hyaluronic Acid Hydrogel for Retinal Tissue Engineering Biomaterial and the Influence of Substrate Stress Relaxation on Retinal Pigment Epithelial Cells

Cell therapies for age-related macular degeneration (AMD) treatment have been developed by integrating hydrogel-based biomaterials. Until now, cell activity has been observed only in terms of the modulus of the hydrogel. In addition, cell behavior has only been observed in the 2D environment of the hydrogel and the 3D matrix. As time-dependent stress relaxation is considered a significant mechanical cue for the control of cellular activities, it is important to optimize hydrogels for retinal tissue engineering (TE) by applying this viewpoint. Herein, a gellan Gum (GG)/Hyaluronic acid (HA) hydrogel was fabricated using a facile physical crosslinking method. The physicochemical and mechanical properties were controlled by forming a different composition of GG and HA. The characterization was performed by conducting a mass swelling study, a sol fraction study, a weight loss test, a viscosity test, an injection force study, a compression test, and a stress relaxation analysis. The biological activity of the cells encapsulated in 3D constructs was evaluated by conducting a morphological study, a proliferation test, a live/dead analysis, histology, immunofluorescence staining, and a gene expression study to determine the most appropriate material for retinal TE biomaterial. Hydrogels with moderate amounts of HA showed improved physicochemical and mechanical properties suitable for injection into the retina. Moreover, the time-dependent stress relaxation property of the GG/HA hydrogel was enhanced when the appropriate amount of HA was loaded. In addition, the cellular compatibility of the GG/HA hydrogel in in vitro experiments was significantly improved in the fast-relaxing hydrogel. Overall, these results demonstrate the remarkable potential of GG/HA hydrogel as an injectable hydrogel for retinal TE and the importance of the stress relaxation property when designing retinal TE hydrogels. Therefore, we believe that GG/HA hydrogel is a prospective candidate for retinal TE biomaterial.

Hydroxysafflor Yellow A (HSYA) Protects Endplate Chondrocytes Against IL-1β-Induced Injury Through Promoting Autophagy

Background

Intervertebral disc degeneration (IDD) refers to intractable pain in patients' waist and legs, which is caused by internal structural disorder and degeneration of intervertebral. This disease severely affects the quality-of-life of people. It has been reported that hydroxysafflor yellow A (HSYA), the active ingredient in safflower extract, could inhibit IL-1β-induced apoptosis of endplate chondrocytes. However, the mechanism by which HSYA regulates the occurrence and progression of IDD remains unclear.

Methods

Rat endplate chondrocytes were isolated from the intervertebral disc. Next, toluidine blue staining and collagen II immunofluorescence staining were used to identify endplate chondrocytes. Then, MDC staining was used to detect the autophagy of endplate chondrocytes. In addition, Western blot was used to measure the expression of cleaved caspase 3, LC-3I/II and ATG7 in endplate chondrocytes.

Results

IL-1β obviously inhibited the viability and proliferation of endplate chondrocytes, while these phenomena were notably reversed by HSYA. Additionally, HSYA was able to inhibit IL-1β-induced apoptosis of endplate chondrocytes. Moreover, HSYA protected endplate chondrocytes against IL-1β-induced inflammation via inducing autophagy.

Conclusion

HSYA protected rat endplate chondrocytes against IL-1β-induced injury via promoting autophagy. Therefore, the present study might provide some theoretical basis for exploring novel and effective methods for patients with IDD.

Development of an Intervertebral Disc for Cervical Spondylosis Composed of Seeded Biomaterials

Most of the current artificial disc prosthesis presented a restricted range of motion. Here we propose the design of a novel intervertebral disc composed of carbon fiber, hyaluronic methylcellulose hydrogel loaded with mesenchymal stem cells and polycaprolactone. The prosthesis was biomechanically evaluated under two static physiological conditions to study the mechanical influence of the material on the device. The results obtained in the simulations showed a not only a congruent behavior with preclinical condition, but also that the proposed materials met the desired biomechanical properties Clinical Relevance- Cervical spondylosis is a degenerative disease of the human spine that causes wear and tear of the cervical intervertebral discs. Nowadays, the proposed surgical solutions do not allow fully recovery of normal movement because the surgical intervention do not emulate the natural range of motion, may lack shock absorption mechanisms, show signs of fatigue over time affecting its durability, and do not have good bone adhesion. Therefore, hypermobility and problems of heterotopic ossification may restrict the range of motion.

Mesenchymal Stem Cell-Derived Exosomes and Intervertebral Disc Regeneration: Review

Intervertebral disc degeneration (IVDD) is a common cause of lower back pain (LBP), which burdens individuals and society as a whole. IVDD occurs as a result of aging, mechanical trauma, lifestyle factors, and certain genetic abnormalities, leads to loss of nucleus pulposus, alteration in the composition of the extracellular matrix, excessive oxidative stress, and inflammation in the intervertebral disc. Pharmacological and surgical interventions are considered a boon for the treatment of IVDD, but the effectiveness of those strategies is limited. Mesenchymal stem cells (MSCs) have recently emerged as a possible promising regenerative therapy for IVDD due to their paracrine effect, restoration of the degenerated cells, and capacity for differentiation into disc cells. Recent investigations have shown that the pleiotropic effect of MSCs is not related to differentiation capacity but is mediated by the secretion of soluble paracrine factors. Early studies have demonstrated that MSC-derived exosomes have therapeutic potential for treating IVDD by promoting cell proliferation, tissue regeneration, modulation of the inflammatory response, and reduced apoptosis. This paper highlights the current state of MSC-derived exosomes in the field of treatment of IVDD with further possible future developments, applications, and challenges.

The co-influence of hyaluronic acid and collagen on the development of an engineered annulus tissue model with bone marrow stromal cells

Inveterbral disc degeneration is a significant musculoskeletal disease that brings huge burden of pain, disability, psychological and social consequences to the affected population worldwide with treatments that only alleviate the pain but does not address the underlying biological problems. For the past decades, tissue engineering of the disc has been investigated with Annulus Fibrosus been one of the complicated disc component to be engineered. With the limited source of annulus cells, bone marrow stromal cells have been frequently investigated as a potental cell candidate to develop an annulus fibrosus-like tissue which often require a multi-disclipinary effort to achieve. The extracellular matrix of Annulus Fibrosus is largely make up of collagen and proteoglycan which is still unclear how these matrix proteins could influence the bone marrow stromal cells towards constructing a AF-like tissue. In this study, we adopted a coiled hydrogel microfiber that resembles the micro-architecture of the native AF tissue to encapsulate bone marrow stromal cells and incorporated collagen type 1 and hyaluronic acid which later demonstrated that the co-presence of hyaluronic acid and collagen could potentially upregulated AF-associated biomarkers and protease expression which are critical for later development of an engineered AF tissue construct.

Critical Review of the State-of-the-Art on Lumbar Percutaneous Cement Discoplasty

Interbody fusion is the gold standard surgery to treat lumbar disc degeneration disease but can be a high-risk procedure in elderly and polymorbid patients. Percutaneous Cement Discoplasty (PCD) is a minimally invasive technique developed to treat advanced stage of disc degeneration exhibiting a vacuum phenomenon. A patient-specific stand-alone spacer is created by filling the disc with polymethylmethacrylate cement, allowing to recover the disc height and improve the patient’s conditions. As it has recently been introduced in the lumbar spine, this review aims to present a transversal state-of-the-art of the surgery from its clinical practice and outcome to biomechanical and engineering topics. The literature was searched across multiple databases using predefined keywords over no limited period of time. Papers about vertebroplasty were excluded. Among 466 identified papers, the relevant ones included twelve clinical papers reporting the variations of the surgical technique, follow-up and complications, four papers reporting biomechanical ex vivo and numerical tests, and four letters related to published clinical papers. Papers presenting the operative practice are reported, as well as follow-ups up to four years. The papers found, consistently reported that PCD significantly improved the clinical status of the patients and maintained it after two years. Spine alignment was impacted by PCD: the sacral slope was significantly reduced, and disc height increased. The foramen opening correlated to the volume of injected cement. Substitutes to the acrylic cement exhibited better osteointegration and mechanical properties closer to bone tissue. Finally, limitations and risks of the surgery are discussed as well as potential improvements such as the development of new filling materials with better mechanical properties and biological integration or the investigation of the inner disc.

Icariin regulates stem cell migration for endogenous repair of intervertebral disc degeneration by increasing the expression of chemotactic cytokines

Background

Icariin (ICA) can promote the migration and bone formation of bone marrow mesenchymal stem cells. This study explored a potential role of ICA in recruiting stem cell niches (SCNs) within the intervertebral disc region (ISN)-derived stem cells (ISN-SCs) to treat intervertebral disc degeneration (IVDD).

Materials and methods

EdU staining, transwell, and wound healing tests were used to analyze the function of ICA on ISN-SCs proliferation and migration ability. Simultaneously, the IVDD rat model was constructed by the acupuncture and divided into Sham, Sham + ICA, IVDD, and IVDD + ICA groups. H&E and PAS staining were performed to detect the pathological changes of IVDD tissues. Immunofluorescence was performed to discover relevant marker expression on the surface of stem cells in the IVDD tissues. Western blot and qPCR were executed to find the protein and mRNA expression of related cytokines in the IVDD tissues.

Results

ISN-SCs treated with 1 μM ICA obtained the better ability of proliferation and migration. H&E staining showed that the annulus fibrosus in the IVDD group was obviously hyperplasia with cavities and fissures; the nucleus pulposus was reduced. PAS staining showed that the content of polysaccharides was significantly reduced in the nucleus pulposus of IVDD group. However, the ICA treatment alleviated the pathological trends of the IVDD tissues. Simultaneously, ICA treatment increased significantly the expression of stem cells and IGF-1, TGF-β, SDF-1, CCL-5, Collagen I, Collagen II, Aggrecan, and SOX9 in IVDD tissues.

Conclusions

ICA treatment promoted the migration of stem cell in IVDD by increasing the expression of chemotactic cytokines, including IGF-1, TGF-β, SDF-1, and CCL-5.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-022-03544-x.

Cyanidin-3-glucoside protects against high glucose-induced injury in human nucleus pulposus cells by regulating the Nrf2/HO-1 signaling

Cyanidin-3-glucoside (C3G) is a well-known natural anthocyanin with antioxidant and anti-inflammatory properties. In this study, we explored the role and action mechanism of C3G in high glucose (HG)-induced damage of human nucleus pulposus cells (HNPCs). Cell viability was assessed by CCK-8 assay. TUNEL assay was performed for detecting apoptotic rate. Western blot was performed to determine the expression levels of cl-caspase-3, caspase-3, Bax, Bim, collagen II, aggrecan, MMP-3, MMP-13, and ADAMTS5. ROS generation was analyzed using DCFH-DA staining. The Nrf2 was knocked down or overexpressed in HNPCs through transfection with si-Nrf2 or pcDNA3.0-Nrf2. C3G treatment (12.5, 25, and 50 μM) improved cell viability of HNPCs under HG condition. HG-induced cell apoptosis of HNPCs was attenuated by C3G with decreased apoptotic rate and relative levels of cl-caspase-3/caspase-3, Bax, and Bim. C3G treatment caused significant increase in expression levels of collagen II and aggrecan and decrease in the relative levels of MMP-3, MMP-13, and ADAMTS5. After treatment with C3G, ROS generation in HNPCs was markedly reduced. Treatment with N-Acetylcysteine (NAC) reversed HG-induced cell apoptosis and extracellular matrix (ECM) degradation. C3G treatment induced the expression of Nrf2 and HO-1 in HG-induced HNPCs. Moreover, knockdown of Nrf2 reversed the inhibitory effect of C3G on ROS production. Summarily, C3G exerted a protective effect on ROS-mediated cellular damage in HNPCs under HG condition, which was attributed to the induction of the Nrf2/HO-1 signaling pathway.

Cell sources proposed for nucleus pulposus regeneration

Lower back pain (LBP) occurs in 80% of adults in their lifetime; resulting in LBP being one of the biggest causes of disability worldwide. Chronic LBP has been linked to the degeneration of the intervertebral disc (IVD). The current treatments for chronic back pain only provide alleviation of symptoms through pain relief, tissue removal, or spinal fusion; none of which target regenerating the degenerate IVD. As nucleus pulposus (NP) degeneration is thought to represent a key initiation site of IVD degeneration, cell therapy that specifically targets the restoration of the NP has been reviewed here. A literature search to quantitatively assess all cell types used in NP regeneration was undertaken. With key cell sources: NP cells; annulus fibrosus cells; notochordal cells; chondrocytes; bone marrow mesenchymal stromal cells; adipose-derived stromal cells; and induced pluripotent stem cells extensively analyzed for their regenerative potential of the NP. This review highlights: accessibility; expansion capability in vitro; cell survival in an IVD environment; regenerative potential; and safety for these key potential cell sources. In conclusion, while several potential cell sources have been proposed, iPSC may provide the most promising regenerative potential.

Proper animal experimental designs for preclinical research of biomaterials for intervertebral disc regeneration

Low back pain is a vital musculoskeletal disease that impairs life quality, leads to disability and imposes heavy economic burden on the society, while it is greatly attributed to intervertebral disc degeneration (IDD). However, the existing treatments, such as medicines, chiropractic adjustments and surgery, cannot achieve ideal disc regeneration. Therefore, advanced bioactive therapies are implemented, including stem cells delivery, bioreagents administration, and implantation of biomaterials etc. Among these researches, few reported unsatisfying regenerative outcomes. However, these advanced therapies have barely achieved successful clinical translation. The main reason for the inconsistency between satisfying preclinical results and poor clinical translation may largely rely on the animal models that cannot actually simulate the human disc degeneration. The inappropriate animal model also leads to difficulties in comparing the efficacies among biomaterials in different reaches. Therefore, animal models that better simulate the clinical charateristics of human IDD should be acknowledged. In addition, in vivo regenerative outcomes should be carefully evaluated to obtain robust results. Nevertheless, many researches neglect certain critical characteristics, such as adhesive properties for biomaterials blocking annulus fibrosus defects and hyperalgesia that is closely related to the clinical manifestations, e.g., low back pain. Herein, in this review, we summarized the animal models established for IDD, and highlighted the proper models and parameters that may result in acknowledged IDD models. Then, we discussed the existing biomaterials for disc regeneration and the characteristics that should be considered for regenerating different parts of discs. Finally, well-established assays and parameters for in vivo disc regeneration are explored.

Two dimensional automatic active shape model of degenerative disc repaired by low-intensity laser

OBJECTIVE

Intervertebral disc degeneration is the main factor causing low back pain, and the related long-term treatment can improve the situation of degeneration. This study aimed to investigate the effect of low-intensity laser irradiation on the repair of degenerative intervertebral disc by two dimensional automatic active shape model (2D-AASM).

METHODS

Nine Bama miniature pigs were randomly divided into three groups: control group (Con), model group (Mod) and laser treatment group (Las). After one month, the discs were treated with low-energy laser for another month. MRI was performed for one month, and the statistical shape model and 2D-AASM of intervertebral disc were established based on the minimum description length method.

RESULTS

The model established by the proposed method is more accurate and the segmentation result is more accurate. From the segmented T2-weighted image, the signal intensity of the Mod group decreased significantly, and the signal intensity in the Las group was moderate and high compared with the Mod group. The HE staining display the structure of Con group was damaged, and the construction of Las group was restored compared with Mod group.

CONCLUSIONS

The 2D-AASM method effectively improves the accuracy of intervertebral disc segmentation. The low-intensity laser has a protective effect on the repair of the degenerative intervertebral disc.

The Application of Mesenchymal Stromal Cells and Their Homing Capabilities to Regenerate the Intervertebral Disc

Chronic low back pain (LBP) remains a challenging condition to treat, and especially to cure. If conservative treatment approaches fail, the current “gold standard” for intervertebral disc degeneration (IDD)-provoked back pain is spinal fusion. However, due to its invasive and destructive nature, the focus of orthopedic research related to the intervertebral disc (IVD) has shifted more towards cell-based therapeutic approaches. They aim to reduce or even reverse the degenerative cascade by mimicking the human body’s physiological healing system. The implementation of progenitor and/or stem cells and, in particular, the delivery of mesenchymal stromal cells (MSCs) has revealed significant potential to cure the degenerated/injured IVD. Over the past decade, many research groups have invested efforts to find ways to utilize these cells as efficiently and sustainably as possible. This narrative literature review presents a summary of achievements made with the application of MSCs for the regeneration of the IVD in recent years, including their preclinical and clinical applications. Moreover, this review presents state-of-the-art strategies on how the homing capabilities of MSCs can be utilized to repair damaged or degenerated IVDs, as well as their current limitations and future perspectives.

Advances in Tissue Engineering for Disc Repair

Intervertebral disc (IVD) degeneration is a leading cause of chronic low back pain (LBP) that results in serious disability and significant economic burden. IVD degeneration alters the disc structure and spine biomechanics, resulting in subsequent structural changes throughout the spine. Currently, treatments of chronic LBP due to IVD degeneration include conservative treatments, such as pain medication and physiotherapy, and surgical treatments, such as removal of herniated disc without or with spinal fusion. However, none of these treatments can completely restore a degenerated disc and its function. Thus, although the exact pathogenesis of disc degeneration remains unclear, there are studies examining the effectiveness of biological approaches, such as growth factor injection, gene therapy, and cell transplantation, in promoting IVD regeneration. Furthermore, tissue engineering using a combination of cell transplantation and biomaterials has emerged as a promising new approach for repair or restoration of degenerated discs. The main purpose of this review was to provide an overview of the current status of tissue engineering applications for IVD regenerative therapy by performing literature searches using PubMed. Significant advances in tissue engineering have opened the door to a new generation of regenerative therapies for the treatment of chronic discogenic LBP.

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.

Therapeutic effect of the injectable thermosensitive hydrogel loaded with SHP099 on intervertebral disc degeneration

AIMS

Intervertebral disc (IVD) degeneration (IDD), a common musculoskeletal disease with limited self-healing ability, is challenging to treat. The development of innovative therapies to reverse IDD depends on the elucidation of its regulatory mechanisms. Therefore, the role of Src homology region 2-containing protein tyrosine phosphatase 2 (SHP2) in the pathogenesis of IDD and the therapeutic effect of its small-molecule inhibitor, SHP099, were investigated.

MATERIALS AND METHODS

The expression of SHP2 by nucleus pulposus (NP) cells in IVD was investigated in vitro and in vivo, and its molecular mechanism in IDD was explored using transfection technology. Injectable N-isopropylacrylamide-based thermosensitive hydrogels were synthesized for SHP099 delivery.

KEY FINDINGS

SHP2 was highly expressed in degenerated IVDs, where its overexpression in NP cells inhibited the expression of Sry-related HMG box-9 (Sox9), leading to the decreased expression of key proteins (collagen II and aggrecan) and consequently to IDD. SHP099 reversed the degeneration of NP cells in vitro. Moreover, its administration in rats via the injectable thermosensitive hydrogel had a therapeutic effect on IDD.

SIGNIFICANCE

Our results suggest that SHP2 is a key factor in IDD progression, and SHP099 inhibits both its expression and NP cell degeneration. Therefore, SHP099 delivery via injectable thermosensitive hydrogels is a potential treatment strategy for IDD.

Intervertebral Disc Regeneration Using Stem Cell/Growth Factor-Loaded Porous Particles with a Leaf-Stacked Structure

Although biological therapies based on growth factors and transplanted cells have demonstrated some positive outcomes for intervertebral disc (IVD) regeneration, repeated injection of growth factors and cell leakage from the injection site remain considerable challenges for human therapeutic use. Herein, we prepare human bone marrow-derived mesenchymal stem cells (hBMSCs) and transforming growth factor-β3 (TGF-β3)-loaded porous particles with a unique leaf-stack structural morphology (LSS particles) as a combination bioactive delivery matrix for degenerated IVD. The LSS particles are fabricated with clinically acceptable biomaterials (polycaprolactone and tetraglycol) and procedures (simple heating and cooling). The LSS particles allow sustained release of TGF-β3 for 18 days and stable cell adhesiveness without additional modifications of the particles. On the basis of in vitro and in vivo studies, it was observed that the hBMSCs/TGF-β3-loaded LSS particles can provide a suitable milieu for chondrogenic differentiation of hBMSCs and effectively induce IVD regeneration in a beagle dog model. Thus, therapeutically loaded LSS particles offer the promise of an effective bioactive delivery system for regeneration of various tissues including IVD.

[Effects of lentivirus-mediated insulin-like growth factor 1 and platelet derived growth factor genes on nucleus pulposus tissue of human degenerated intervertebral disc]

Objective

To observe and compare the cytological and biological differences between human normal and degenerated nucleus pulposus (NP), and to investigate the repair effect of insulin-like growth factor 1 (IFG-1) and platelet derived growth factor (PDGF) on human degenerated NP.

Methods

Human degenerative and normal NP tissues were obtained from operative patients, a portion of which were processed into tissue sections and HE staining was performed to observe the morphological changes of nucleus pulposus cells (NPCs) before and after degeneration of NP. Immunohistochemistry staining was used to determine the expression levels of collagen type Ⅰ, collagen type Ⅱ, B-cell lymphoma 2 (Bcl-2), Bcl-2 associated X (Bax) proteins. Another portion of tissues were isolated and cultured and NPCs morphology was observed under inverted microscope. Western blot analysis was used to detect collagen type Ⅱ protein expression. Then, the gene transfection experiments were launched, including 4 groups, with group A designed as degenerated NPCs only, and groups B, C, and D of degenerated NPCs transfected with IGF-1 gene lentiviral particles, PDGF gene lentiviral particles, and lentiviral particles carrying IGF-1 and PDGF double genes, respectively. At 21 days after transfection, the cell morphology of each group was observed under inverted microscope, the positive rates of IGF-1 and PDGF of each group were measured by flow cytometry, and the expression of collagen type Ⅱ protein was detected by using immunohistochemistry staining and Western blot.

Results

HE staining showed that there were a large number of notochordal cells and a small number of chondrocytes in the central NP tissue of normal group, while the NPCs in degeneration group were significantly reduced, and a large proportion of fibrocartilage tissues were found in NP tissue. Immunohistochemistry staining showed that the percentages of collagen type Ⅰ and Bax protein-positive cells in degeneration group were significantly higher than those of normal group, while the percentages of collagen type Ⅱ and Bcl-2 protein-positive cells were significantly lower than those of normal group ( P<0.05). Western blot showed that the relative expression level of collagen type Ⅱ protein in degeneration group was significantly lower than that in normal group ( t=65.493, P=0.000). At 21 days after gene transfection, compared with group A, the cell viability of groups B, C, and D increased and the morphology became more regular. Flow cytometry showed that the percentages of IGF-1-positive cells in groups B and D were significantly higher than that in group A, and the percentages of PDGF-positive cells in groups C and D were significantly higher than that in group A ( P<0.05). Immunohistochemistry staining showed that the positive stainings of collagen type Ⅱ in groups A, B, C, and D was (±), (+), (+), and (++), respectively. Western blot showed that the relative expression of collagen type Ⅱ protein in groups A, B, C, and D increased by degrees, and the differences between groups were significant ( P<0.05).

Conclusion

Both IGF-1 and PDGF can reverse the degeneration of intervertebral discs NPCs and they have synergistic effects, providing experimental basis for its application in clinical treatment approaches for degenerative disc disease.

Quantitative Single-Cell Transcript Assessment of Biomarkers Supports Cellular Heterogeneity in the Bovine IVD

Severe and chronic low back pain is often associated with intervertebral disc (IVD) degeneration. While imposing a considerable socio-economic burden worldwide, IVD degeneration is also severely impacting on the quality of life of affected individuals. Cell-based regenerative medicine approaches have moved into clinical trials, yet IVD cell identities in the mature disc remain to be fully elucidated and tissue heterogeneity exists, requiring a better characterization of IVD cells. The bovine coccygeal IVD is an accepted research model to study IVD mechano-biology and disc homeostasis. Recently, we identified novel IVD biomarkers in the outer annulus fibrosus (AF) and nucleus pulposus (NP) of the mature bovine coccygeal IVD through RNA in situ hybridization (AP-RISH) and z-proportion test. Here we follow up on Lam1, Thy1, Gli1, Gli3, Noto, Ptprc, Scx, Sox2 and Zscan10 with fluorescent RNA in situ hybridization (FL-RISH) and confocal microscopy. This permits sub-cellular transcript localization and the addition of quantitative single-cell derived values of mRNA expression levels to our previous analysis. Lastly, we used a Gaussian mixture modeling approach for the exploratory analysis of IVD cells. This work complements our earlier cell population proportion-based study, confirms the previously proposed biomarkers and indicates even further heterogeneity of cells in the outer AF and NP of a mature IVD.