Immunomodulation of Human Mesenchymal Stem/Stromal Cells in Intervertebral Disc Degeneration: Insights From a Proinflammatory/Degenerative Ex Vivo Model

Orthobiologic Management Options for Degenerative Disc Disease

Degenerative disc disease (DDD) is a pervasive condition that limits quality of life and burdens economies worldwide. Conventional pharmacological treatments primarily aimed at slowing the progression of degeneration have demonstrated limited long-term efficacy and often do not address the underlying causes of the disease. On the other hand, orthobiologics are regenerative agents derived from the patient's own tissue and represent a promising emerging therapy for degenerative disc disease. This review comprehensively outlines the pathophysiology of DDD, highlighting the inadequacies of existing pharmacological therapies and detailing the potential of orthobiologic approaches. It explores advanced tools such as platelet-rich plasma and mesenchymal stem cells, providing a historical overview of their development within regenerative medicine, from foundational in vitro studies to preclinical animal models. Moreover, the manuscript delves into clinical trials that assess the effectiveness of these therapies in managing DDD. While the current clinical evidence is promising, it remains insufficient for routine clinical adoption due to limitations in study designs. The review emphasizes the need for further research to optimize these therapies for consistent and effective clinical outcomes, potentially revolutionizing the management of DDD and offering renewed hope for patients.

Progress in the study of molecular mechanisms of intervertebral disc degeneration

Degenerative intervertebral disc disease (IVDD) is one of the main spinal surgery, conditions, which markedly increases the incidence of low back pain and deteriorates the patient's quality of life, and it imposes significant social and economic burdens. The molecular pathology of IVDD is highly complex and multilateral however still not ompletely understood. New findings indicate that IVDD is closely associated with inflammation, oxidative stress, cell injury and extracellular matrix metabolismdysregulation. Symptomatic management is the main therapeutic approach adopted for IVDD, but it fails to address the basic pathological changes and the causes of the disease. However, research is still focusing on molecular aspects in terms of gene expression, growth factors and cell signaling pathways in an attempt to identify specific molecular targets for IVDD treatment. The paper summarizes the most recent achievements in molecularunderstanding of the pathogenesis of IVDD and gives evidence-based recommendations for clinical practice.

Progress in regulating inflammatory biomaterials for intervertebral disc regeneration

Intervertebral disc degeneration (IVDD) is rising worldwide and leading to significant health issues and financial strain for patients. Traditional treatments for IVDD can alleviate pain but do not reverse disease progression, and surgical removal of the damaged disc may be required for advanced disease. The inflammatory microenvironment is a key driver in the development of disc degeneration. Suitable anti-inflammatory substances are critical for controlling inflammation in IVDD. Several treatment options, including glucocorticoids, non-steroidal anti-inflammatory drugs, and biotherapy, are being studied for their potential to reduce inflammation. However, anti-inflammatories often have a short half-life when applied directly and are quickly excreted, thus limiting their therapeutic effects. Biomaterial-based platforms are being explored as anti-inflammation therapeutic strategies for IVDD treatment. This review introduces the pathophysiology of IVDD and discusses anti-inflammatory therapeutics and the components of these unique biomaterial platforms as comprehensive treatment systems. We discuss the strengths, shortcomings, and development prospects for various biomaterials platforms used to modulate the inflammatory microenvironment, thus providing guidance for future breakthroughs in IVDD treatment.

A new strategy for intervertebral disc regeneration: The synergistic potential of mesenchymal stem cells and their extracellular vesicles with hydrogel scaffolds

Intervertebral disc degeneration (IDD) is a disease that severely affects spinal health and is prevalent worldwide. Mesenchymal stem cells (MSCs) and their derived extracellular vesicles (EVs) have regenerative potential and have emerged as promising therapeutic tools for treating degenerative discs. However, challenges such as the harsh microenvironment of degenerated intervertebral discs and EVs' limited stability and efficacy have hindered their clinical application. In recent years, hydrogels have attracted much attention in the field of IDD therapy because they can mimic the physiologic microenvironment of the disc and provide a potential solution by providing a suitable growth environment for MSCs and EVs. This review introduced the biological properties of MSCs and their derived EVs, summarized the research on the application of MSCs and EVs in IDD, summarized the current clinical trial studies of MSCs and EVs, and also explored the mechanism of action of MSCs and EVs in intervertebral discs. In addition, plenty of research elaborated on the mechanism of action of different classified hydrogels in tissue engineering, the synergistic effect of MSCs and EVs in promoting intervertebral disc regeneration, and their wide application in treating IDD. Finally, the challenges and problems still faced by hydrogel-loaded MSCs and EVs in the treatment of IDD are summarized, and potential solutions are proposed. This paper outlines the synergistic effects of MSCs and EVs in treating IDD in combination with hydrogels and aims to provide theoretical references for future related studies.

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.

Effective Modulation of Inflammation and Oxidative Stress for Enhanced Regeneration of Intervertebral Discs Using 3D Porous Hybrid Protein Nanoscaffold

Degeneration of fibrocartilaginous tissues is often associated with complex pro-inflammatory factors. These include reactive oxygen species (ROS), cell-free nucleic acids (cf-NAs), and epigenetic changes in immune cells. To effectively control this complex inflammatory signaling, it developed an all-in-one nanoscaffold-based 3D porous hybrid protein (3D-PHP) self-therapeutic strategy for treating intervertebral disc (IVD) degeneration. The 3D-PHP nanoscaffold is synthesized by introducing a novel nanomaterial-templated protein assembly (NTPA) strategy. 3D-PHP nanoscaffolds that avoid covalent modification of proteins demonstrate inflammatory stimuli-responsive drug release, disc-mimetic stiffness, and excellent biodegradability. Enzyme-like 2D nanosheets incorporated into nanoscaffolds further enabled robust scavenging of ROS and cf-NAs, reducing inflammation and enhancing the survival of disc cells under inflammatory stress in vitro. Implantation of 3D-PHP nanoscaffolds loaded with bromodomain extraterminal inhibitor (BETi) into a rat nucleotomy disc injury model effectively suppressed inflammation in vivo, thus promoting restoration of the extracellular matrix (ECM). The resulting regeneration of disc tissue facilitated long-term pain reduction. Therefore, self-therapeutic and epigenetic modulator-encapsulated hybrid protein nanoscaffold shows great promise as a novel approach to restore dysregulated inflammatory signaling and treat degenerative fibrocartilaginous diseases, including disc injuries, providing hope and relief to patients worldwide.

High-Tech Methods of Cytokine Imbalance Correction in Intervertebral Disc Degeneration

An important mechanism for the development of intervertebral disc degeneration (IDD) is an imbalance between anti-inflammatory and pro-inflammatory cytokines. Therapeutic and non-therapeutic approaches for cytokine imbalance correction in IDD either do not give the expected result, or give a short period of time. This explains the relevance of high-tech medical care, which is part of specialized care and includes the use of new resource-intensive methods of treatment with proven effectiveness. The aim of the review is to update knowledge about new high-tech methods based on cytokine imbalance correction in IDD. It demonstrates promise of new approaches to IDD management in patients resistant to previously used therapies, including: cell therapy (stem cell implantation, implantation of autologous cultured cells, and tissue engineering); genetic technologies (gene modifications, microRNA, and molecular inducers of IDD); technologies for influencing the inflammatory cascade in intervertebral discs mediated by abnormal activation of inflammasomes; senolytics; exosomal therapy; and other factors (hypoxia-induced factors; lysyl oxidase; corticostatin; etc.).

Human 3D nucleus pulposus microtissue model to evaluate the potential of pre-conditioned nasal chondrocytes for the repair of degenerated intervertebral disc

Introduction: An in vitro model that appropriately recapitulates the degenerative disc disease (DDD) microenvironment is needed to explore clinically relevant cell-based therapeutic strategies for early-stage degenerative disc disease. We developed an advanced 3D nucleus pulposus (NP) microtissues (µT) model generated with cells isolated from human degenerating NP tissue (Pfirrmann grade: 2-3), which were exposed to hypoxia, low glucose, acidity and low-grade inflammation. This model was then used to test the performance of nasal chondrocytes (NC) suspension or spheroids (NCS) after pre-conditioning with drugs known to exert anti-inflammatory or anabolic activities. Methods: NPµTs were formed by i) spheroids generated with NP cells (NPS) alone or in combination with ii) NCS or iii) NC suspension and cultured in healthy or degenerative disc disease condition. Anti-inflammatory and anabolic drugs (amiloride, celecoxib, metformin, IL-1Ra, GDF-5) were used for pre-conditioning of NC/NCS. The effects of pre-conditioning were tested in 2D, 3D, and degenerative NPµT model. Histological, biochemical, and gene expression analysis were performed to assess matrix content (glycosaminoglycans, type I and II collagen), production and release of inflammatory/catabolic factors (IL-6, IL-8, MMP-3, MMP-13) and cell viability (cleaved caspase 3). Results: The degenerative NPµT contained less glycosaminoglycans, collagens, and released higher levels of IL-8 compared to the healthy NPµT. In the degenerative NPµT, NCS performed superior compared to NC cell suspension but still showed lower viability. Among the different compounds tested, only IL-1Ra pre-conditioning inhibited the expression of inflammatory/catabolic mediators and promoted glycosaminoglycan accumulation in NC/NCS in DDD microenvironment. In degenerative NPµT model, preconditioning of NCS with IL-1Ra also provided superior anti-inflammatory/catabolic activity compared to non-preconditioned NCS. Conclusion: The degenerative NPµT model is suitable to study the responses of therapeutic cells to microenvironment mimicking early-stage degenerative disc disease. In particular, we showed that NC in spheroidal organization as compared to NC cell suspension exhibited superior regenerative performance and that IL-1Ra pre-conditioning of NCS could further improve their ability to counteract inflammation/catabolism and support new matrix production within harsh degenerative disc disease microenvironment. Studies in an orthotopic in vivo model are necessary to assess the clinical relevance of our findings in the context of IVD repair.

Low Back Pain, Disability, and Quality of Life One Year following Intradiscal Injection of Autologous Bone Marrow Aspirate Concentrate

Introduction

Degenerative disc disease is a common cause of chronic low back pain. Surgical intervention is an invasive treatment associated with high costs. There is growing interest in regenerative medicine as a less invasive but direct disc treatment for chronic discogenic low back pain.

Objective

To evaluate clinical improvement of primary discogenic low back pain with intradiscal injection of autologous bone marrow aspirate concentrate (BMAC). Study Design. Prospective cohort study. Setting. Single, multiphysician center. Patients. 32 adult patients undergoing intradiscal injection of autologous BMAC for the treatment of primary discogenic low back pain. Interventions. Intradiscal injection of autologous BMAC. Main Outcome Measures. Primary outcome measure is visual analog back pain scale (VAS back pain). Secondary outcome measures include ODI, VAS leg pain, and EQ-5D-5L scores. Outcomes were compared from baseline to 1 year.

Results

Thirty-two patients (56.3% male) with a mean age of 45.9 years were enrolled, giving 92 treated levels. Mean VAS back and leg pain scores improved from 5.4 to 3.0 (p < 0.001) and 2.8 to 1.3 (p = 0.005), respectively. Mean ODI scores decreased from 33.5 to 21.1 (p < 0.001), and EQ-5D-5L scores improved from 0.69 to 0.78 (p = 0.001). Using established MCID values, 59.4% had clinically significant improvement in VAS back pain, 43.8% in VAS leg pain, and 56.3% in ODI scores.

Conclusion

Intradiscal injection of autologous BMAC significantly improved low back pain, disability, and quality of life at one year. This study suggests that intradiscal BMAC has the potential to be an effective nonsurgical treatment for chronic discogenic low back pain.

Application of stem cells combined with biomaterial in the treatment of intervertebral disc degeneration

As the world population is aging, intervertebral disc degeneration (IDD) is becoming a global health issue of increasing concern. A variety of disc degeneration diseases (DDDs) have been proven to be associated with IDD, and these illnesses have significant adverse effects on both individuals and society. The application of stem cells in regenerative medicine, such as blood and circulation, has been demonstrated by numerous studies. Similarly, stem cells have made exciting progress in the treatment of IDD. However, due to complex anatomical structures and functional requirements, traditional stem cell injection makes it difficult to meet people's expectations. With the continuous development of tissue engineering and biomaterials, stem cell combined with biomaterials has far more prospects than before. This review aims to objectively and comprehensively summarize the development of stem cells combined with contemporary biomaterials and the difficulties that need to be overcome.

The Influence of Intervertebral Disc Microenvironment on the Biological Behavior of Engrafted Mesenchymal Stem Cells

Intervertebral disc degeneration is the main cause of low back pain. Traditional treatment methods cannot repair degenerated intervertebral disc tissue. The emergence of stem cell therapy makes it possible to regenerate and repair degenerated intervertebral disc tissue. At present, mesenchymal stem cells are the most studied, and different types of mesenchymal stem cells have their own characteristics. However, due to the harsh and complex internal microenvironment of the intervertebral disc, it will affect the biological behaviors of the implanted mesenchymal stem cells, such as viability, proliferation, migration, and chondrogenic differentiation, thereby affecting the therapeutic effect. This review is aimed at summarizing the influence of each intervertebral disc microenvironmental factor on the biological behavior of mesenchymal stem cells, so as to provide new ideas for using tissue engineering technology to assist stem cells to overcome the influence of the microenvironment in the future.

Pyroptosis and Intervertebral Disc Degeneration: Mechanistic Insights and Therapeutic Implications

Low back pain (LBP) is a common problem worldwide, resulting in great patient suffering and great challenges for the social health system. Intervertebral disc (IVD) degeneration (IVDD) is widely acknowledged as one of the key causes of LBP. Accumulating evidence suggests that aberrant pyroptosis of IVD cells is involved in the pathogenesis of IVDD progression, however, the comprehensive roles of pyroptosis in IVDD have not been fully established, leaving attempts to treat IVDD with anti-pyroptosis approaches questionable. In this review, we summarize the characteristics of pyroptosis and emphasize the effects of IVD cell pyroptosis on the pathological progression of IVDD, including secretion of cytokines, nucleus pulposus cell apoptosis and autophagy, accelerated extracellular matrix degradation, annulus fibrosus rupture, cartilage endplate calcification, vascularization, sensory and sympathetic fiber neoinnervation, and infiltrating lymphatic vessels. Finally, we discuss several interventions used to treat IVDD by targeting pyroptosis. This review provides novel insights into the crucial role of IVD cell pyroptosis in IVDD pathogenesis, and could be informative for developing novel therapeutic approaches for IVDD and LBP.

An in vitro 3D annulus fibrosus cell culture model with type I collagen: An examination of cell-matrix interactions

Background

Disorders of the intervertebral disc (IVD) are widely known to result in low back pain; one of the most common debilitating conditions worldwide. As a multifaceted condition, both inflammatory environment and mechanical factors can play a crucial role in IVD damage, and in particular, in the annulus fibrosus (AF), the highly collagenous outer ring of the IVD. As a result, a better understanding of how cells from the IVD, and specifically the AF, interact and respond to their environment is imperative.

Goal

The goal of this study is to use collagen type I as an in vitro three-dimensional extracellular matrix for AF cells of IVD and briefly examine both the cellular and mechanical effect of exposure to an inflammatory stimulant.

Methods

We utilized type I collagen as a 3D in vitro model material for culturing AF cells of Sprague Dawley rat tail IVDs.

Results

We showed that the cultured cells are viable and metabolically active; these cells also induced a distinct and significant contraction on their collagen matrix. Furthermore, to demonstrate potential versatility of our model our model and its versatility, we used lipopolysaccharide (LPS), as a known inflammatory stimulant in IVDs, to manipulate the cells and their interaction. LPS treatment resulted in detectable changes to the contraction cells induced on the collagen matrix and affected the mechanical properties of these constructs.

Should Degenerated Intervertebral Discs of Patients with Modic Type 1 Changes Be Treated with Mesenchymal Stem Cells?

Low back pain (LBP) has been among the leading causes of disability for the past 30 years. This highlights the need for improvement in LBP management. Many clinical trials focus on developing treatments against degenerative disc disease (DDD). The multifactorial etiology of DDD and associated risk factors lead to a heterogeneous patient population. It comes as no surprise that the outcomes of clinical trials on intradiscal mesenchymal stem cell (MSC) injections for patients with DDD are inconsistent. Intradiscal MSC injections have demonstrated substantial pain relief and significant disability-related improvements, yet they have failed to regenerate the intervertebral disc (IVD). Increasing evidence suggests that the positive outcomes in clinical trials might be attributed to the immunomodulatory potential of MSCs rather than to their regenerative properties. Therefore, patient stratification for inflammatory DDD phenotypes may (i) better serve the mechanisms of action of MSCs and (ii) increase the treatment effect. Modic type 1 changes—pathologic inflammatory, fibrotic changes in the vertebral bone marrow—are frequently observed adjacent to degenerated IVDs in chronic LBP patients and represent a clinically distinct subpopulation of patients with DDD. This review discusses whether degenerated IVDs of patients with Modic type 1 changes should be treated with an intradiscal MSC injection.

Application of stem cells in the repair of intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common disease that increases with age, and its occurrence is stressful both psychologically and financially. Stem cell therapy for IDD is emerging. For this therapy, stem cells from different sources have been proven in vitro, in vivo, and in clinical trials to relieve pain and symptoms, reverse the degeneration cascade, delay the aging process, maintain the spine shape, and retain mechanical function. However, further research is needed to explain how stem cells play these roles and what effects they produce in IDD treatment. This review aims to summarize and objectively analyse the current evidence on stem cell therapy for IDD.

Interleukin-1β More Than Mechanical Loading Induces a Degenerative Phenotype in Human Annulus Fibrosus Cells, Partially Impaired by Anti-Proteolytic Activity of Mesenchymal Stem Cell Secretome

Mesenchymal stem/stromal cell (MSC)–based therapies for low back pain and intervertebral disc (IVD) degeneration have been emerging, despite the poor knowledge of their full mechanism of action. As failure of the annulus fibrosus (AF) is often associated with IVD herniation and inflammation, the objective of the present study was to investigate the impact of the MSC secretome on human AF cells exposed to mechanical loading and a pro-inflammatory environment. Human AF cells isolated from IVD biopsies from patients with adolescent idiopathic scoliosis (AIS) or disc degeneration (DD) were exposed to physiological cyclic tensile strain (CTS) for 72 h in a custom-made device, with or without interleukin (IL)-1β medium supplementation. AF cells stimulated with CTS + IL-1β were then treated with secretome from IL-1β–preconditioned MSCs for 48 h. AF cell metabolic activity, gene expression, protein secretion, matrix metalloproteinase (MMP) activity, and tissue inhibitor of MMPs (TIMP) concentration were evaluated. Expanded AF cells from AIS and DD patients revealed similar metabolic activity and gene expression profiles. CTS stimulation upregulated collagen type I (COL1A1) expression, while IL-1β significantly stimulated IL-6, IL-8, MMP-1, and MMP-3 gene expression and prostaglandin E₂ production by AF cells but downregulated COL1A1. The combination of CTS + IL-1β had a similar outcome as IL-1β alone, accompanied by a significant upregulation of elastin. The MSC secretome did not show any immunomodulatory effect on CTS + IL-1β–stimulated AF cells but significantly decreased MMP-1, MMP-2, MMP-3, and MMP-9, while increasing the production of TIMP-1. The obtained results demonstrate a stronger impact of the inflammatory milieu on human AF cells than upper physiologic mechanical stress. In addition, a new MSC mechanism of action in degenerated IVD consisting of the modulation of AF MMP activity was also evidenced, contributing to the advancement of knowledge in AF tissue metabolism.

Immunomodulatory effects of mesenchymal stem cells in peripheral nerve injury

Various immune cells and cytokines are present in the aftermath of peripheral nerve injuries (PNI), and coordination of the local inflammatory response is of great significance for the recovery of PNI. Mesenchymal stem cells (MSCs) exhibit immunosuppressive and anti-inflammatory abilities which can accelerate tissue regeneration and attenuate inflammation, but the role of MSCs in the regulation of the local inflammatory microenvironment after PNI has not been widely studied. Here, we summarize the known interactions between MSCs, immune cells, and inflammatory cytokines following PNI with a focus on the immunosuppressive role of MSCs. We also discuss the immunomodulatory potential of MSC-derived extracellular vesicles as a new cell-free treatment for PNI.

New hope for intervertebral disc degeneration: bone marrow mesenchymal stem cells and exosomes derived from bone marrow mesenchymal stem cell transplantation

Bone marrow mesenchymal stem cells (BMSCs), multidirectional cells with self-renewal capacity, can differentiate into many cell types and play essential roles in tissue healing and regenerative medicine. Cell experiments and in vivo research in animal models have shown that BMSCs can repair degenerative discs by promoting cell proliferation and expressing extracellular matrix (ECM) components, such as type II collagen and protein-polysaccharides. Delaying or reversing the intervertebral disc (IVD) degeneration (IDD) process at an etiological level may be an effective strategy. However, despite increasingly in-depth research, some deficiencies in cell transplantation timing and strategy remain, preventing the clinical application of cell transplantation. Exosomes exhibit the characteristics of the mother cells from which they were secreted and can inhibit nucleus pulposus (NP) cell (NPC) apoptosis and delay IDD through intercellular communication. Furthermore, the use of exosomes effectively avoids problems associated with cell transplantation, such as immune rejection. This manuscript introduces almost all of the BMSCs and exosomes derived from BMSCs (BMSCs-Exos) described in the IDD literature. Many challenges regarding the use of cell transplantation and therapeutic exosome intervention for IDD remain to be overcome.

Hypoxic Preconditioning Enhances Bone Marrow-Derived Mesenchymal Stem Cell Survival in a Low Oxygen and Nutrient-Limited 3D Microenvironment

OBJECTIVE

Skeletal tissues such as intervertebral disc and articular cartilage possess limited innate potential to regenerate, in part due to their avascularity and low cell density. Despite recent advances in mesenchymal stem cell (MSC)-based disc and cartilage regeneration, key challenges remain, including the sensitivity of these cells to in vivo microenvironmental stress such as low oxygen and limited nutrition. The objective of this study was to investigate whether preconditioning with hypoxia and/or transforming growth factor-β 3 (TGF-β3) can enhance MSC survival and extracellular matrix production in a low oxygen and nutrient-limited microenvironment.

DESIGN

MSCs from multiple bovine donors were preconditioned in monolayer in normoxia or hypoxia, with or without TGF-β3, and the global effects on gene expression were examined using microarrays. Subsequently, the effects of preconditioning on MSC survival and extracellular matrix production were examined using low oxygen and nutrient-limited pellet culture experiments.

RESULTS

Hypoxic preconditioning resulted in upregulation of genes associated with growth, cell-cell signaling, metabolism, and cell stress response pathways, and significantly enhanced MSC survival for all donors in low oxygen and nutrient-limited pellet culture. In contrast, TGF-β3 preconditioning diminished survival. The nature and magnitude of the effects of preconditioning with either hypoxia or TGF-β3 on glycosaminoglycan production were donor dependent.

CONCLUSIONS

These results strongly support the use of hypoxic preconditioning to improve postimplantation MSC survival in avascular tissues such as disc and cartilage.

ADSC-Based Cell Therapies for Musculoskeletal Disorders: A Review of Recent Clinical Trials

Recently published clinical trials involving the use of adipose-derived stem cells (ADSCs) indicated that approximately one-third of the studies were conducted on musculoskeletal disorders (MSD). MSD refers to a wide range of degenerative conditions of joints, bones, and muscles, and these conditions are the most common causes of chronic disability worldwide, being a major burden to the society. Conventional treatment modalities for MSD are not sufficient to correct the underlying structural abnormalities. Hence, ADSC-based cell therapies are being tested as a form of alternative, yet more effective, therapies in the management of MSDs. Therefore, in this review, MSDs subjected to the ADSC-based therapy were further categorized as arthritis, craniomaxillofacial defects, tendon/ligament related disorders, and spine disorders, and their brief characterization as well as the corresponding conventional therapeutic approaches with possible mechanisms with which ADSCs produce regenerative effects in disease-specific microenvironments were discussed to provide an overview of under which circumstances and on what bases the ADSC-based cell therapy was implemented. Providing an overview of the current status of ADSC-based cell therapy on MSDs can help to develop better and optimized strategies of ADSC-based therapeutics for MSDs as well as help to find novel clinical applications of ADSCs in the near future.

Exosome: Function and Application in Inflammatory Bone Diseases

In the skeletal system, inflammation is closely associated with many skeletal disorders, including periprosthetic osteolysis (bone loss around orthopedic implants), osteoporosis, and rheumatoid arthritis. These diseases, referred to as inflammatory bone diseases, are caused by various oxidative stress factors in the body, resulting in long-term chronic inflammatory processes and eventually causing disturbances in bone metabolism, increased osteoclast activity, and decreased osteoblast activity, thereby leading to osteolysis. Inflammatory bone diseases caused by nonbacterial factors include inflammation- and bone resorption-related processes. A growing number of studies show that exosomes play an essential role in developing and progressing inflammatory bone diseases. Mechanistically, exosomes are involved in the onset and progression of inflammatory bone disease and promote inflammatory osteolysis, but specific types of exosomes are also involved in inhibiting this process. Exosomal regulation of the NF-κB signaling pathway affects macrophage polarization and regulates inflammatory responses. The inflammatory response further causes alterations in cytokine and exosome secretion. These signals regulate osteoclast differentiation through the receptor activator of the nuclear factor-kappaB ligand pathway and affect osteoblast activity through the Wnt pathway and the transcription factor Runx2, thereby influencing bone metabolism. Overall, enhanced bone resorption dominates the overall mechanism, and over time, this imbalance leads to chronic osteolysis. Understanding the role of exosomes may provide new perspectives on their influence on bone metabolism in inflammatory bone diseases. At the same time, exosomes have a promising future in diagnosing and treating inflammatory bone disease due to their unique properties.

Intervertebral Disc Degeneration Models for Pathophysiology and Regenerative Therapy -Benefits and Limitations

Aim:This review summarized the recent intervertebral disc degeneration (IDD) models and described their advantages and potential disadvantages, aiming to provide an overview for the current condition of IDD model establishment and new ideas for new strategies development of the treatment and prevention of IDD.Methods:The database of PubMed was searched up to May 2021 with the following search terms: nucleus pulposus, annulus fibrosus, cartilage endplate, intervertebral disc(IVD), intervertebral disc degeneration, animal model, organ culture, bioreactor, inflammatory reaction, mechanical stress, pathophysiology, epidemiology. Any IDD model-related articles were collected and summarized.Results:The best IDD model should have the features of repeatability, measurability and controllability. There are a lot of aspects to be considered in the selection of animals. Mice, rats and rabbits are low-cost and easy to access. However, their IVD size and shape are more different from human anatomy than pigs, cattle, sheep and goats. Organ culture models and animal models are two options in model establishment for IDD. The IVD organ culture model can put the studying variables into the controllable system for transitional research. Unlike the animal model, the organ culture model can only be used to evaluate the short-term effects and it is not applicable in simulating the complex process of IDD. Similarly, the animal models induced by different methods also have their advantages and disadvantages. For studying the mechanism of IDD and the corresponding treatment and prevention strategies, the selection of model should be individualized based on the purpose of each study.Conclusions:Various models have different characteristics and scope of application due to their different rationales and methods of construction. Currently, there is no experimental model that can perfectly mimic the degenerative process of human IVD. Personalized selection of appropriate model based on study purpose and experimental designing can enhance the possibility to obtain reliable and real results.

Investigating the physiological relevance of ex vivo disc organ culture nutrient microenvironments using in silico modeling and experimental validation

BACKGROUND

Ex vivo disc organ culture systems have become a valuable tool for the development and pre-clinical testing of potential intervertebral disc (IVD) regeneration strategies. Bovine caudal discs have been widely selected due to their large availability and comparability to human IVDs in terms of size and biochemical composition. However, despite their extensive use, it remains to be elucidated whether their nutrient microenvironment is comparable to human degeneration.

AIMS

This work aims to create the first experimentally validated in silico model which can be used to predict and characterize the metabolite concentrations within ex vivo culture systems.

MATERIALS & METHODS

Finite element models of cultured discs governed by previously established coupled reaction-diffusion equations were created using COMSOL Multiphysics. Experimental validation was performed by measuring oxygen, glucose and pH levels within discs cultured for 7 days, in a static compression bioreactor.

RESULTS

The in silico model was successfully validated through good agreement between the predicted and experimentally measured concentrations. For an ex vivo organ cultured in high glucose medium (4.5 g/L or 25 mM) and normoxia, a larger bovine caudal disc (Cd1-2 to Cd3-4) had a central concentration of ~2.6 %O2, ~8 mM of glucose and a pH value of 6.7, while the smallest caudal discs investigated (Cd6-7 and Cd7-8), had a central concentration of ~6.5 %O2, ~12 mM of glucose and a pH value of 6.9.

DISCUSSION

This work advances the knowledge of ex vivo disc culture microenvironments and highlights a critical need for optimization and standardization of culturing conditions.

CONCLUSION

Ultimately, for assessment of cell-based therapies and successful clinical translation based on nutritional demands, it is imperative that the critical metabolite values within organ cultures (minimum glucose, oxygen and pH values) are physiologically relevant and comparable to the stages of human degeneration.

Stem Cells and Intervertebral Disc Regeneration Overview-What They Can and Can't Do

BACKGROUND

Low back pain (LPB) is the main cause of disability worldwide with enormous socioeconomic burdens. A major cause of LBP is intervertebral disc degeneration (IDD): a chronic, progressive process associated with exhaustion of the resident cell population, tissue inflammation, degradation of the extracellular matrix and dehydration of the nucleus pulposus. Eventually, IDD may lead to serious sequelae including chronic LBP, disc herniation, segmental instability, and spinal stenosis, which may require invasive surgical interventions. However, no treatment is actually able to directly tackle IDD and hamper the degenerative process. In the last decade, the intradiscal injection of stem cells is raising as a promising approach to regenerate the intervertebral disc. This review aims to describe the rationale behind a regenerative stem cell therapy for IDD as well as the effect of stem cells following their implantation in the disc environment according to preclinical studies. Furthermore, actual clinical evidence and ongoing trials will be discussed, taking into account the future perspective and current limitations of this cutting-edge therapy.

METHODS

A literature analysis was performed for this narrative review. A database search of PubMed, Scopus and ClinicalTrials.gov was conducted using "stem cells" combined with "intervertebral disc", "degeneration" and "regeneration" without exclusion based on publication date. Articles were firstly screened on a title-abstract basis and, subsequently, full-text were reviewed. Both preclinical and clinical studies have been included.

RESULTS

The database search yielded recent publications from which the narrative review was completed.

CONCLUSIONS

Based on available evidence, intradiscal stem cell therapy has provided encouraging results in terms of regenerative effects and reduction of LBP. However, multicenter, prospective randomized trials are needed in order confirm the safety, efficacy and applicability of such a promising treatment.

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.

Cell-based strategies for IVD repair: clinical progress and translational obstacles

Intervertebral disc (IVD) degeneration is a major cause of low back pain, a prevalent and chronic condition that has a striking effect on quality of life. Currently, no approved pharmacological interventions or therapies are available that prevent the progressive destruction of the IVD; however, regenerative strategies are emerging that aim to modify the disease. Progress has been made in defining promising new treatments for disc disease, but considerable challenges remain along the entire translational spectrum, from understanding disease mechanism to useful interpretation of clinical trials, which make it difficult to achieve a unified understanding. These challenges include: an incomplete appreciation of the mechanisms of disc degeneration; a lack of standardized approaches in preclinical testing; in the context of cell therapy, a distinct lack of cohesion regarding the cell types being tested, the tissue source, expansion conditions and dose; the absence of guidelines regarding disease classification and patient stratification for clinical trial inclusion; and an incomplete understanding of the mechanisms underpinning therapeutic responses to cell delivery. This Review discusses current approaches to disc regeneration, with a particular focus on cell-based therapeutic strategies, including ongoing challenges, and attempts to provide a framework to interpret current data and guide future investigational studies.

Allogeneic mesenchymal precursor cells treatment for chronic low back pain associated with degenerative disc disease: a prospective randomized, placebo-controlled 36-month study of safety and efficacy

BACKGROUND CONTEXT PURPOSE

Evaluate the safety and efficacy of a single intradiscal injection of STRO-3+ adult allogeneic mesenchymal precursor cells (MPCs) combined with hyaluronic acid (HA) in subjects with chronic low back pain (CLBP) associated with degenerative disc disease (DDD) through 36-month follow-up.

STUDY DESIGN/SETTING

A multicenter, randomized, controlled study conducted at 13 clinical sites (12 in the United States and 1 in Australia).

SUBJECT SAMPLE

A total of 100 subjects with chronic low back pain associated with moderate DDD (modified Pfirrmann score of 3-6) at one level from L1 to S1 for at least 6 months and failing 3 months of conservative treatment, including physical therapy were randomized in a 3:3:2:2 ratio to receive 6 million MPCs with HA, 18 million MPCs with HA, HA vehicle control, or saline control (placebo) treatment.

OUTCOME MEASURES

Subjects were clinically and radiographically evaluated at 1, 3, 6, 12, 24, and 36 months postinjection. Subject-reported outcomes including adverse events, LBP on a Visual Analog Scale (VAS), Oswestry Disability Index (ODI), SF-36 and Work Productivity and Activity Index were collected.

METHODS

Clinical and radiographic measures were collected at each visit. All randomized subjects were included in the safety assessments and analyzed based on the treatment received. Safety assessments included assessments of AEs, physical and radiographic examinations and laboratory testing. Efficacy assessments evaluated changes in VAS, ODI, and modified Pfirrmann (MP) scores between all active and control groups, respectively. Assessments included least squares mean (Mean), LS mean change from baseline (Mean Change) and responder analyses in order to assess the clinical significance of observed changes from baseline. The population for efficacy assessments was adjusted for the confounding effects of post-treatment interventions (PTIs). This study was conducted under an FDA Investigational New Drug application sponsored and funded by Mesoblast.

RESULTS

There were significant differences between the control and MPC groups for improvement in VAS and ODI. The PTI-corrected VAS and ODI Means and Mean Change analyses; the proportion of subjects with VAS ≥30% and ≥50% improvement from baseline; absolute VAS score ≤20; and ODI reduction ≥10 and ≥15 points from baseline showed MPC therapy superior to controls at various time points through 36 months. Additionally, the proportion of subjects achieving the minimally important change and clinically significant change composite endpoints for the MPC groups was also superior compared with controls at various time points from baseline to 36 months. There were no significant differences in change in MP score from baseline across the groups. There were also no statistically significant differences in change in modified MP score at the level above or below the level treated between study arms. Both the procedure and treatment were well tolerated and there were no clinical symptoms of immune reaction to allogeneic MPCs. There was a low rate of Treatment Emergent Adverse Events (TEAEs) and Serious Adverse Events, and the rates of these events in the MPC groups were not significantly different from the control groups. One TEAE of severe back pain was possibly related to study agent and one TEAE of implantation site infection was considered to be related to the study procedure.

CONCLUSIONS

Results provide evidence that intradiscal injection of MPCs could be a safe, effective, durable, and minimally invasive therapy for subjects who have CLBP associated with moderate DDD.

The role of IL-1β and TNF-α in intervertebral disc degeneration

Low back pain (LBP), a prevalent and costly disease around the world, is predominantly caused by intervertebral disc (IVD) degeneration (IDD). LBP also presents a substantial burden to public health and the economy. IDD is mainly caused by aging, trauma, genetic susceptibility, and other factors. It is closely associated with changes in tissue structure and function, including progressive destruction of the extracellular matrix (ECM), enhanced senescence, disc cell death, and impairment of tissue biomechanical function. The inflammatory process, exacerbated by cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), are considered to be the key mediators of IDD and LBP. IL-1β and TNF-α are the most important proinflammatory cytokines, as they have powerful proinflammatory activities and can promote the secretion of a variety of proinflammatory mediators. They are also upregulated in the degenerative IVDs, and they are closely related to various pathological IDD processes, including inflammatory response, matrix destruction, cellular senescence, autophagy, apoptosis, pyroptosis, and proliferation. Therefore, anti-IL-1β and anti-TNF-α therapies may have the potential to alleviate disc degeneration and LBP. In this paper, we reviewed the expression pattern and signal transduction pathways of IL-1β and TNF-α, and we primarily focused on their similar and different roles in IDD. Because IL-1β and TNF-α inhibition have the potential to alleviate IDD, an in-depth understanding of the role of IL-1β and TNF-α in IDD will benefit the development of new treatment methods for disc degeneration with IL-1β and TNF-α at the core.

Combined Hydrogel and Mesenchymal Stem Cell Therapy for Moderate-Severity Disc Degeneration in Goats

Intervertebral disc degeneration is a cascade of cellular, structural, and biomechanical changes that is strongly implicated as a cause of low-back pain. Current treatment strategies have poor long-term efficacy as they seek only to alleviate symptoms without preserving or restoring native tissue structure and function. The objective of this study was to evaluate the efficacy of a combined triple interpenetrating network hydrogel (comprising dextran, chitosan, and teleostean) and mesenchymal stem cell (MSC) therapy targeting moderate-severity disc degeneration in a clinically relevant goat model. Degeneration was induced in lumbar discs of 10 large frame goats by injection of chondroitinase ABC. After 12 weeks, degenerate discs were treated by injection of either hydrogel alone or hydrogel seeded with allogeneic, bone marrow-derived MSCs. Untreated healthy and degenerate discs served as controls, and animals were euthanized 2 weeks after treatment. Discs exhibited a significant loss of disc height 12 weeks after degeneration was induced. Two weeks after treatment, discs that received the combined hydrogel and MSC injection exhibited a significant, 10% improvement in disc height index, as well as improvements in histological condition. Discs that were treated with hydrogel alone exhibited reduced tumor necrosis factor-α expression in the nucleus pulposus (NP). Microcomputed tomography imaging revealed that the hydrogel remained localized to the central NP region of all treated discs after 2 weeks of unrestricted activity. These encouraging findings motivate further, longer term studies of therapeutic efficacy of hydrogel and MSC injections in this large animal model. Impact statement Low-back pain is the leading cause of disability worldwide, and degeneration of the intervertebral discs is considered to be one of the most common reasons for low-back pain. Current treatment strategies focus solely on alleviation of symptoms, and there is a critical need for new treatments that also restore disc structure and function. In this study, using a clinically relevant goat model of moderate-severity disc degeneration, we demonstrate that a combined interpenetrating network hydrogel and mesenchymal stem cell therapy provides acute improvements in disc height, histological condition, and local inflammation.

The association of peripheral immune markers with brain cortical thickness and surface area in South African people living with HIV

A spectrum of cognitive impairments known as HIV-associated neurocognitive disorders (HAND) are consequences of the effects of HIV-1 within the central nervous system. Regardless of treatment status, an aberrant chronic neuro-immune regulation is a crucial contributor to the development of HAND. However, the extent to which inflammation affects brain structures critical for cognitive status remains unclear. The present study aimed to determine associations of peripheral immune markers with cortical thickness and surface area. Participants included 65 treatment-naïve HIV-positive individuals and 26 HIV-negative controls. Thickness and surface area of all cortical regions were derived using automated parcellation of T1-weighted images acquired at 3 T. Peripheral immune markers included C-C motif ligand 2 (CCL2), matrix metalloproteinase 9 (MMP9), neutrophil gelatinase-associated lipocalin (NGAL), thymidine phosphorylase (TYMP), transforming growth factor (TGF)-β1, and vascular endothelial growth factor (VEGF), which were measured using enzyme-linked immunosorbent assays. Associations of these markers with thickness and surface area of cortical regions were evaluated. A mediation analysis examined whether associations of inflammatory markers with cognitive functioning were mediated by brain cortical thickness and surface area. After controlling for multiple comparisons, higher NGAL was associated with reduced thickness of the bilateral orbitofrontal cortex in HIV-positive participants. The association of NGAL with worse motor function was mediated by cortical thickness of the bilateral orbitofrontal region. Taken together, this study suggests that NGAL plays a potential role in the neuropathophysiology of neurocognitive impairments of HIV.

Therapeutic Potential of Extracellular Vesicles in Degenerative Diseases of the Intervertebral Disc

Extracellular vesicles (EVs) are lipid membrane particles carrying proteins, lipids, DNA, and various types of RNA that are involved in intercellular communication. EVs derived from mesenchymal stem cells (MSCs) have been investigated extensively in many different fields due to their crucial role as regeneration drivers, but research for their use in degenerative diseases of the intervertebral disc (IVD) has only started recently. MSC-derived EVs not only promote extracellular matrix synthesis and proliferation in IVD cells, but also reduce apoptosis and inflammation, hence having multifunctional beneficial effects that seem to be mediated by specific miRNAs (such as miR-233 and miR-21) within the EVs. Aside from MSC-derived EVs, IVD-derived EVs (e.g., stemming from notochordal cells) also have important functions in IVD health and disease. This article will summarize the current knowledge on MSC-derived and IVD-derived EVs and will highlight areas of future research, including the isolation and analysis of EV subpopulations or exposure of MSCs to cues that may enhance the therapeutic potential of released EVs.

Stem Cell Senescence: the Obstacle of the Treatment of Degenerative Disk Disease

Intervertebral disc (IVD) has a pivotal role in the maintenance of flexible motion. IVD degeneration is one of the primary causes of low back pain and disability, which seriously influences patients' health, and increases the family and social economic burden. Recently, stem cell therapy has been proven to be more effective on IVD degeneration disease. However, stem cell senescence is the limiting factor in the IVD degeneration treatment. Senescent stem cells have a negative effect on the self-repair on IVD degeneration. In this review, we delineate that the factors such as telomerase shortening, DNA damage, oxidative stress, microenvironment and exosomes will induce stem cell aging. Recent studies tried to delay the aging of stem cells by regulating the expression of aging-related genes and proteins, changing the activity of telomerase, improving the survival microenvironment of stem cells and drug treatment. Understanding the mechanism of stem cell aging and exploring new approaches to delay or reverse stem cell aging asks for research on the repair of the degenerated disc.

TRIM32 triggers β-catenin signaling through ubiquitylation of AXIN1 to promote inflammatory factor-induced apoptosis of rat nucleus pulposus cells

The dysregulation of ubiquitin ligase is the cause of many human diseases. Tripartite motif protein 32 (TRIM32) is an E3 ubiquitin ligase whose role in nucleus pulposus (NP) cell apoptosis is unclear. The expression of TRIM family protein and β-catenin in 40 NP tissue samples was detected by RT-PCR. Interleukin (IL)-1β or tumor necrosis factor (TNF)-α was used to treat rat NP cells. Knockdown and overexpression of Trim32 were achieved using specific siRNA and recombinant plasmids. Western blotting, RT-PCR, and flow cytometry were used to assess the expression of TRIM32/β-catenin and the apoptosis rate of NP cells. Coimmunoprecipitation was adopted to analyze the possible interactions between AXIN1 and TRIM32. In clinical samples, TRIM32 expression was of positive relevance with the expression of CTNNB1 (β-catenin). In vitro, apoptosis of IL-1β- or TNF-α-treated rat NP cells was induced through upregulated Trim32 expression and activated β-catenin signaling, whereas Trim32 siRNA and inhibition of β-catenin reversed the induction effect of cytokines. Further studies indicated that TRIM32 activated the β-catenin signaling pathway through ubiquitination of AXIN1, thereby regulating apoptosis. Collectively, this study reveals that TRIM32 promotes inflammatory factor-induced apoptosis of rat NP cells, in part by direct degradation of AXIN1 to trigger β-catenin signaling.

Bone marrow-derived mesenchymal stem cells in three-dimensional co-culture attenuate degeneration of nucleus pulposus cells

Intervertebral disc degeneration (IDD) is an irreversible aging-associated clinical condition of unclear etiology. Mesenchymal stem cells (MSCs) have the potential to delay IDD, but the mechanisms by which MSCs attenuate senescence-related degeneration of nucleus pulposus cells (NPCs) remain uncertain. The present study employed a three-dimensional (3D) co-culture system to explore the influence of MSCs on NPC degeneration induced by TNF-α in rat cells. We found that co-culture with bone marrow-derived MSCs (BMSCs) reduced senescence-associated β-galactosidase expression, increased cell proliferation, decreased matrix metalloproteinase 9, increased Coll-IIa production, and reduced TGFβ/NF-κB signaling in senescent NPCs. In addition, expression of zinc metallopeptidase STE24 (ZMPSTE24), whose dysfunction is related to premature cell senescence and aging, was decreased in senescent NPCs but restored upon BMSC co-culture. Accordingly, ZMPSTE24 overexpression in NPCs inhibited the pro-senescence effects of TGFβ/NF-κB activation upon TNF-α stimulation, while both CRISPR/Cas9-mediated silencing and pharmacological ZMPSTE24 inhibition prevented those effects. Ex-vivo experiments on NP explants provided supporting evidence for the protective effect of MSCs against NPC senescence and IDD. Although further molecular studies are necessary, our results suggest that MSCs may attenuate or prevent NP fibrosis and restore the viability and functional status of NPCs through upregulation of ZMPSTE24.

Interaction between Mesenchymal Stem Cells and Intervertebral Disc Microenvironment: From Cell Therapy to Tissue Engineering

Low back pain (LBP) in one of the most disabling symptoms affecting nearly 80% of the population worldwide. Its primary cause seems to be intervertebral disc degeneration (IDD): a chronic and progressive process characterized by loss of viable cells and extracellular matrix (ECM) breakdown within the intervertebral disc (IVD) especially in its inner region, the nucleus pulposus (NP). Over the last decades, innovative biological treatments have been investigated in order to restore the original healthy IVD environment and achieve disc regeneration. Mesenchymal stem cells (MSCs) have been widely exploited in regenerative medicine for their capacity to be easily harvested and be able to differentiate along the osteogenic, chondrogenic, and adipogenic lineages and to secrete a wide range of trophic factors that promote tissue homeostasis along with immunomodulation and anti-inflammation. Several in vitro and preclinical studies have demonstrated that MSCs are able to acquire a NP cell-like phenotype and to synthesize structural components of the ECM as well as trophic and anti-inflammatory mediators that may support resident cell activity. However, due to its unique anatomical location and function, the IVD presents distinctive features: avascularity, hypoxia, low glucose concentration, low pH, hyperosmolarity, and mechanical loading. Such conditions establish a hostile microenvironment for both resident and exogenously administered cells, which limited the efficacy of intradiscal cell therapy in diverse investigations. This review is aimed at describing the characteristics of the healthy and degenerated IVD microenvironment and how such features influence both resident cells and MSC viability and biological activity. Furthermore, we focused on how recent research has tried to overcome the obstacles coming from the IVD microenvironment by developing innovative cell therapies and functionalized bioscaffolds.

Stem Cell Therapies for Treatment of Discogenic Low Back Pain: a Comprehensive Review

PURPOSE OF REVIEW

Discogenic low back pain (DLBP) stems from pathology in one or more intervertebral discs identified as the root cause of the pain. It is the most common type of chronic low back pain (LBP), representing 26-42% of attributable cases.

RECENT FINDINGS

The clinical presentation of DLBP includes increased pain when sitting, coughing, or sneezing, and experiencing relief when standing or ambulating. Dermatomal radiation of pain to the lower extremity and neurological symptoms including numbness, motor weakness, and urinary or fecal incontinence are signs of advanced disease with disc prolapse, nerve root compression, or spinal stenosis. Degenerative disc disease is caused by both a decrease in disc nutrient supply causing decreased oxygen, lowered pH, and lessened ability of the intervertebral disc (IVD) to respond to increased load or injury; moreover, changes in the extracellular matrix composition cause weakening of the tissue and skewing the extracellular matrix's (ECM) harmonious balance between catabolic and anabolic factors for cell turnover in favor of catabolism. Thus, the degeneration of the disc causes a shift from type II to type I collagen expression by NP cells and a decrease in aggrecan synthesis leads to dehydrated matrix cells ultimately with loss of swelling pressure needed for mechanical support. Cell-based therapies such as autologous nucleus pulposus cell re-implantation have in animal models and human trials shown improvements in LBP score, retention of hydration in IVD, and increased disc height. Percutaneously delivered multipotent mesenchymal stem cell (MSC) therapy has been proposed as a potential means to uniquely ameliorate discogenic LBP holistically through three mechanisms: mitigation of primary nociceptive disc pain, slow or reversal of the catabolic metabolism, and restoration of disc tissue. Embryonic stem cells (ESCs) can differentiate into cells of all three germ layers in vitro, but their use is hindered related to ethical concerns, potential for immune rejection after transplantation, disease, and teratoma formation. Another similar approach to treating back pain is transplantation of the nucleus pulposus, which, like stem cell therapy, seeks to address the underlying cause of intervertebral disc degeneration by aiming to reverse the destructive inflammatory process and regenerate the proteoglycans and collagen found in healthy disc tissue. Preliminary animal models and clinical studies have shown mesenchymal stem cell implantation as a potential therapy for IVD regeneration and ECM restoration via a shift towards favorable anabolic balance and reduction of pain.

Macrophages Down-Regulate Gene Expression of Intervertebral Disc Degenerative Markers Under a Pro-inflammatory Microenvironment

Low back pain is a highly prevalent clinical problem and intervertebral disc (IVD) degeneration is now accepted as the major pathophysiological mechanism responsible for this condition. Accumulating evidence suggests that inflammation plays a crucial role in the progression of human IVD degeneration, with macrophages being pointed as the key immune cell players in this process since their infiltration in degenerated IVD samples has been extensively demonstrated. Since they are highly plastic, macrophages can play different roles depending on the microenvironmental cues. The study of inflammation associated with IVD degeneration has been somehow neglected and one of the reasons is related with lack of adequate models. To overcome this, we established and characterized a new model of IVD organ culture under pro-inflammatory conditions to further dissect the role of macrophages in IVD associated immune response. For that, human monocyte-derived macrophages were co-cultured either with bovine caudal IVD punches in the presence of the pro-inflammatory cytokine IL-1β, or IVD-conditioned medium (CM), to investigate how IVD-produced factors influence macrophage phenotype. After 72 h, metabolic activity, gene expression and cytokine profile of macrophages and IVD cells were measured. Our results show that macrophages and IVDs remain metabolically active in the presence of IL-1β, significantly upregulate CCR7 gene expression and increase production of IL-6 on macrophages. When treating macrophages with IL-1β-IVD-CM, CCR7 upregulation follows the same trend, while for IL-6 an opposite effect was observed. On the other hand, macrophages interfere with IVD ECM remodeling, decreasing MMP3 expression and downregulating aggrecan and collagen II gene expression in the presence of IL-1β. Overall, the co-culture model established in this study can be considered a suitable approach to address the cellular and molecular pathways that regulate macrophage-IVD crosstalk, suggesting that degenerated IVD tissue tends to polarize human macrophages toward a more pro-inflammatory profile, which seems to aggravate IVD degeneration. This model could be used to improve the knowledge of the mechanisms that link IVD degeneration and the immune response.

MicroRNA Expression Profiles, Target Genes, and Pathways in Intervertebral Disk Degeneration: A Meta-Analysis of 3 Microarray Studies

BACKGROUND

Determining the expression profile and target genes of microRNA (miRNA) would assist in determining the pathophysiologic pathways in intervertebral disk degeneration (IDD). The aim of this study was to determine the expression profile of miRNA in degenerated intervertebral disks compared with normal healthy intervertebral disks.

METHODS

We conducted a meta-analysis of 3 available miRNA expression datasets to identify a panel of co-deregulated miRNA genes and overlapping biological processes in IDD. Degenerated intervertebral disks were compared with normal healthy disks. We selected 35 miRNA features common to all 3 platforms. Then, we calculated differential expression P values from our unpaired data using metaMA package in R statistical software according to the moderated t test method (Limma). Based on the P values (where the threshold was <0.05), a list of differentially expressed miRNAs was identified.

RESULTS

After normalization and selection of common miRNA features across all 3 platforms, we found a total of 5 differentially expressed miRNAs, among which miR-574-3p, miR-199a-5p, and miR-483-5p were not identified in any individual studies. Our results revealed that miR-199a-5p, miR-574-3p, miR-551a, and miR-640 are commonly upregulated in IDDs compared with control disks, whereas miR-483 is commonly downregulated. Pathway analysis of identified dysregulated miRNAs indicated the involvement of extracellular matrix-receptor interaction, adherens junction, and transforming growth factor-beta signaling pathway in the pathogenesis of IDDs. Moreover, the network of predicted targets for these miRNAs identified most affected target genes as ERBB4 and CLTC.

CONCLUSIONS

We found that the identified miRNAs through meta-analysis are candidate predictive markers for IDDs through different pathways.

Controversies in regenerative medicine: Should intervertebral disc degeneration be treated with mesenchymal stem cells?

Low back pain (LBP) can significantly reduce the quality of life of patients, and has a considerable economic and social impact worldwide. It is commonly associated with disc degeneration, even though many people with degenerate discs are asymptomatic. Degenerate disc disease (DDD), is thus a common term for intervertebral disc (IVD) degeneration associated with LBP. Degeneration is thought to lead to LBP because of nerve ingrowth into the degenerate disc, inflammation, or because degradation of extracellular matrix (ECM) alters spinal biomechanics inappropriately. Thus, while the objectives of some interventions for LBP are to control pain intensity, other interventions aim to deal with the consequences of disc degeneration through stabilizing the disc surgically, by inserting artificial discs or by repairing the disc biologically and preventing progressive IVD degeneration. Despite tremendous research efforts, treatment of LBP through the use of regenerative interventions aiming to repair the IVD is still controversial. The use of mesenchymal stem cells for IVD regeneration in a patient-based case will be discussed by an ensemble of clinicians and researchers.

An ex vivo human placental vessel perfusion method to study mesenchymal stem/stromal cell migration

Background

To initiate tissue repair, mesenchymal stem/stromal cells (MSCs) must enter the blood stream, migrate to the targeted area, cross the endothelial barrier and home to the damaged tissue. This process is not yet fully understood in humans and thus, the aim of this study was to develop an ex vivo placental vessel perfusion method to examine human MSC movement from a blood vessel into human tissue. This will provide a better understanding of MSC migration, movement through the endothelial barrier and engraftment into target tissue, in a setting that more closely represents the in vivo state, compared with conventional in vitro human cell culture models. Moreover, important similarities and differences to animal experimental model systems may be revealed by this method.

Methods

Human placental hTERT transformed MSC lines were labelled with live-cell fluorescence dyes, and then perfused into term human placental blood vessel. After labelled MSCs were perfused into the vessel, the vessel was dissected from the placenta and incubated at cell growth conditions. Following incubation, the vessel was washed thoroughly to remove unattached, labelled MSCs and then snap frozen for sectioning. After sectioning, immunofluorescence staining of the endothelium was carried out to detect if labelled MSCs crossed the endothelial barrier.

Results

Twelve placental vessel perfusions were successfully completed. In eight of the twelve perfused vessels, qualitative assessment of immunofluorescence in sections (n=20, 5 µm sections/vessel) revealed labelled MSCs had crossed the endothelial barrier.

Conclusions

The human placental ex vivo vessel perfusion method could be used to assess human MSC migration into human tissue. Cells of the MSC lines were able to adhere and transmigrate through the endothelial barrier in a manner similar to that of leukocytes. Notably, cells that transmigrated remained in close proximity to the endothelium, which is consistent with the reported MSC vascular niche in placental blood vessels.

Mesenchymal Stromal Cell Secretome: Influencing Therapeutic Potential by Cellular Pre-conditioning

Mesenchymal stromal cells (MSCs) are self-renewing, culture-expandable adult stem cells that have been isolated from a variety of tissues, and possess multipotent differentiation capacity, immunomodulatory properties, and are relatively non-immunogenic. Due to this unique set of characteristics, these cells have attracted great interest in the field of regenerative medicine and have been shown to possess pronounced therapeutic potential in many different pathologies. MSCs' mode of action involves a strong paracrine component resulting from the high levels of bioactive molecules they secrete in response to the local microenvironment. For this reason, MSCs' secretome is currently being explored in several clinical contexts, either using MSC-conditioned media (CM) or purified MSC-derived extracellular vesicles (EVs) to modulate tissue response to a wide array of injuries. Rather than being a constant mixture of molecular factors, MSCs' secretome is known to be dependent on the diverse stimuli present in the microenvironment that MSCs encounter. As such, the composition of the MSCs' secretome can be modulated by preconditioning the MSCs during in vitro culture. This manuscript reviews the existent literature on how preconditioning of MSCs affects the therapeutic potential of their secretome, focusing on MSCs' immunomodulatory and regenerative features, thereby providing new insights for the therapeutic use of MSCs' secretome.

Autogenic mesenchymal stem cells for intervertebral disc regeneration

PURPOSE

A systematic review of the literature was conducted to clarify the outcomes of autologous mesenchymal stem cells (MSC) injections for the regeneration of the intervertebral disc (IVD).

METHODS

The following databases were accessed: PubMed, Medline, CINAHL, Cochrane, Embase and Google Scholar bibliographic databases. Articles including previous or planned surgical interventions were excluded. Only articles reporting percutaneous autologous MSC injection to regenerate IVD in humans were included. We referred to the Coleman Methodology Score for the methodological quality assessment. The statistical analysis was performed using Review Manager Software 5.3.

RESULTS

After the databases search and cross-references of the bibliographies, seven studies were included in the present work. The funnel plot detected low risk of publication bias. The Coleman Methodology Score reported a good result, scoring 61.07 points. A total of 98 patients were enrolled, with 122 treated levels. All the patients underwent conservative therapies prior to injection. A remarkable improvement in the quality of life were reported after the treatment. The average Oswestry Disability Index (ODI) improved from "severe disability" to "minimal disability" at one year follow-up. The visual analogue scale (VAS) showed an improvement of ca. 30% at one year follow-up. Only one case of herniated nucleus pulposus was reported. No other adverse events at the aspiration or injection site were observed.

CONCLUSIONS

This systematic review of the literature proved MSC injection to be a safe and feasible option for intervertebral disc regeneration in the early-degeneration stage patients. Irrespective of the source of the MSCs, an overall clinical and radiological improvement of the patients has been evidenced, as indeed a very low complication rate during the follow-up.

Exosomes in perspective: a potential surrogate for stem cell therapy

Exosomes as a unique subtype of small extracellular vesicles (sEVs) have attracted increasing interest in recent years in the fields of mesenchymal stromal cell (MSC) research. Studies have confirmed that exosomes derived from MSCs preserve immunosuppressive phenotype and can mimic therapeutic benefits of their parent cells. This review briefly summarizes most recent findings on the potential of exosomes as an alternative of therapeutic MSCs, focusing on the role of MSCs and their secreted exosomes in regulation of immune cells, preclinical and clinical evidence of therapeutic outcomes of MSC exosomes, and the biodistribution and pharmacokinetic profile of systemically administered exosomes. It is appreciated that exosomes from MSCs of different sources have variable contents including inflammatory mediators, tropic factors, signaling molecules, and nucleic acids (DNA, mRNA, microRNA and long non-coding RNA). Diverse functions of exosomes derived from different sources are expected. More importantly, exosomes isolated in vitro may not mirror that from in vivo, where donor MSCs are exposed to specific disease or injury-related conditions. Simulating in vivo microenvironment by pretreatment of MSCs with relevant chemical mediators may lead to their secretion of therapeutically more efficient exosomes/sEVs. However, we know very little about the key molecules involved and the differences between exosomes released under different conditions. These issues would be of tremendous interest to preclinical research that pursues exosome biology-underlain therapeutic mechanisms of MSCs. Further studies are expected to demonstrate the superiority of MSC-derived exsomes/sEVs as a pharmaceutical entity with regard to efficacy, safety, and practicability.

Stromal Cell Derived Factor-1-Mediated Migration of Mesenchymal Stem Cells Enhances Collagen Type II Expression in Intervertebral Disc

Intervertebral disc (IVD) degeneration is characterized by an unbalanced cell catabolic/anabolic activity and cell death, resulting in the degradation of extracellular matrix components and water loss. Repopulating the IVD with new cells may help in recovering tissue homeostasis and reverting the degenerative process. In this study the regenerative potential of a hyaluronan (HA)-based chemoattractant delivery system able to recruit mesenchymal stem cells (MSCs) seeded on the cartilaginous endplate (CEP) of IVD was explored. A HA delivery system containing stromal cell derived factor-1 (SDF-1) (5 ng/μL) (HAPSDF5) was injected in the cavity of nucleotomized bovine discs. Human MSCs (1 × 106) were seeded on the opposite CEP and allowed to migrate for up to 21 days. Migration of fluorescently labelled MSCs from CEP toward the IVD was enhanced by HAPSDF5. Likewise, an increase in collagen type II was detected at earlier time points, whereas no effect on proteoglycan content within the nucleotomized IVDs was found. MSCs produced an increased concentration of pro-catabolic factors, such as interleukin (IL)-6, IL-8, and monocyte chemoattractant protein-1 (MCP-1). Overall, this study demonstrates that HAPSDF5 increased MSC recruitment, while the higher number of recruited cells partially contributed to accelerate matrix remodeling in nucleotomized IVDs.

miR-148a inhibits pro-inflammatory cytokines released by intervertebral disc cells by regulating the p38/MAPK pathway

The present study aimed to verify the expression and investigate the role of microRNA (miR)-148a in intervertebral disc degeneration (IDD) and explore the associated underlying mechanisms. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to investigate levels of miR-148a in the peripheral blood mononuclear cells (PBMCs) of patients with IDD. To investigate the role of miR-148a in IDD, a stable miR-148a-overexpression/underexpression human nucleus pulposus (NP) cell line was generated by transfection with miR-148a mimic/inhibitor. Then, NP cells were treated with LPS (10 µM) to induce inflammation. The mRNA expression level of miR-148a in NP cells was determined by RT-qPCR and the expression levels of p38 and p-p38 were measured using western blotting. The mRNA expression and supernatant level of pro-inflammatory cytokines, tumor necrosis factor (TNF-α), interleukin (IL)-1β and IL-6, was evaluated by RT-qPCR and ELISA, respectively. The results indicated that miR-148a was significantly downregulated in the PBMCs of IDD patients compared with healthy controls. In vitro upregulation of miR-148a in LPS-stimulated NP cells, by transfection with miR-148a mimic, resulted in inhibition of p-p38 expression; however, inhibition of miR-148a led to overexpression of p-p38. Meanwhile, the production of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) was significantly reduced in miR-148a-overexpressing LPS-stimulated NP cells and significantly increased in miR-148a-underexpressing NP cells. In conclusion, miR-148a inhibits pro-inflammatory cytokines released by intervertebral disc cells via regulation of the p38/mitogen-activated protein kinase pathway.