Notochordal Cell Matrix As a Therapeutic Agent for Intervertebral Disc Regeneration

Effects of 3D-printed exosome-functionalized brain acellular matrix hydrogel on neuroinflammation in rats following cerebral hemorrhage

BACKGROUND

Exosome-based therapeutics have garnered significant attention for intracerebral hemorrhage (ICH) treatment due to their capacity to regulate metabolic dysregulation, restore cellular homeostasis, and modulate the injury microenvironment via bioactive cargoes such as microRNAs and proteins. However, rapid systemic clearance and enzymatic degradation critically limit their therapeutic efficacy. To address this challenge, we engineered a three-dimensional (3D) bioprinted scaffold capable of encapsulating and sustaining the release of human umbilical cord mesenchymal stem cell-derived exosomes (hUCMSC-exos).

METHODS

Based on previous research [1-3], the scaffold was composed of a decellularized brain matrix (dECM), gelatin-methacryloyl (GelMA), and silk fibroin (SF) crosslinked with a photoinitiator. hUCMSC-exos were precisely incorporated via extrusion-based 3D bioprinting. Release kinetics were assessed via in vitro elution and in vivo imaging. An ICH rat model received stereotaxic implantation of the exosome-laden scaffold (dECM@exo). Neuroinflammatory markers (IL-6, TNF-α, IL-10) and apoptotic activity (JC-1, Annexin V/PI, TUNEL) were quantified. Neurological outcomes were longitudinally evaluated using the modified Longa scale, Bederson scoring, and sensorimotor tests (rotarod, forelimb placement) at 1, 4, 7 and 14 days post-ICH.

RESULTS

dECM@exo demonstrated sustained exosome release over 14 days, significantly promoting neural tissue regeneration while attenuating perihematomal edema. Mechanistically, the scaffold modulated pathological MMP activity and inflammatory cytokine expression, thereby restoring extracellular matrix homeostasis and reducing neuronal apoptosis.

CONCLUSIONS

The findings demonstrate that the 3D biological scaffold dECM@exo effectively maintains microenvironmental homeostasis in the early stages of ICH and improves outcomes associated with the condition. dECM@exo is poised to serve as a robust platform for drug delivery and biotherapy in ICH treatment, offering a viable alternative for managing this condition.

Cartilage Organoids from Articular Chondroprogenitor Cells and Their Potential to Produce Neo-Hyaline Cartilage

INTRODUCTION

The use of autologous human primary articular chondrocytes (hPACs) for repairing damaged cartilage is the golden standard; however, their 2-dimensional (2D) expansion induces dedifferentiation, making it challenging to create hyaline cartilage. Spinner flasks are efficient for generating cartilage organoids, allowing hPACs to proliferate without dedifferentiation; however, porcine notochordal cell-derived matrix (NCM) is needed for aggregation, limiting clinical application. Human articular chondroprogenitor cells (hACPCs) can be expanded many fold while maintaining chondrogenic potential. Therefore, the scalable production of hACPC cartilage organoids without NCM in spinner flasks was investigated in this study.

METHODS

hPAC organoids with NCM and hACPC organoids using bone morphogenetic protein 9 (BMP-9) were produced in spinner flasks in 14 days. Thereafter, approximately 20 organoids were fused in low adhesive wells for 21 days. Organoids underwent mechanical testing, and both organoids and fused constructs were evaluated using biochemical, histological, and immunohistochemical analysis.

RESULTS

The hACPCs self-assembled and synthesized abundant extracellular matrix once stimulated with BMP-9. The hPAC and hACPC organoids showed similar mechanical properties, but hACPC organoids and fused constructs showed a more uniform matrix and cell distribution.

CONCLUSION

The hACPC organoids fused into a neo-hyaline cartilage-like tissue, demonstrating their potential for improved, scalable cartilage tissue repair.

Innovating intervertebral disc degeneration therapy: Harnessing the power of extracellular vesicles

Intervertebral disc degeneration is the leading cause of low back pain, imposing significant burdens on patients, societies, and economies. Advancements in regenerative medicine have spotlighted extracellular vesicles as promising nanoparticles for intervertebral disc degeneration treatment. Extracellular vesicles retain the potential of cell therapy and serve as carriers to deliver their cargo to target cells, thereby regulating cell activity. This review summarizes the biogenesis and molecular composition of extracellular vesicles and explores their therapeutic roles in intervertebral disc degeneration treatment through various mechanisms. These mechanisms include mitigating cell loss and senescence, delaying extracellular matrix degeneration, and modulating the inflammatory microenvironment. Additionally, it highlights recent efforts in engineering extracellular vesicles to enhance their targeting and therapeutic efficacy. The integration of extracellular vesicle-based acellular therapy is anticipated to drive significant advancements in disc regenerative medicine.

The translational potential of this article

Existing clinical treatment strategies often fail to effectively address the challenges associated with regenerating degenerated intervertebral discs. As a new regenerative medicine strategy, the extracellular vesicle strategy avoids the risks associated with cell transplantation and shows great promise in treating intervertebral disc degeneration by carrying therapeutic cargo. This review comprehensively examines the latest research, underlying mechanisms, and therapeutic potential of extracellular vesicles, offering a promising new strategy for intervertebral disc degeneration treatment.

Intervertebral Disc Degeneration and Regeneration: New Molecular Mechanisms and Therapeutics: Obstacles and Potential Breakthrough Technologies

Pain and disability secondary to degenerative disc disease continue to burden the healthcare system, creating an urgent need for effective, disease-modifying therapies. Contemporary research has identified potential therapies that include protein-, cellular- and/or matrix-related approaches; however, none have yet achieved a meaningful clinical impact. The tissue-specific realities of the intervertebral disc create considerable therapeutic challenges due to the disc's location, compartmentalization, hypovascularization and delicate physiological environment. Furthermore, the imaging modalities currently used in practice are largely unable to accurately identify sources of pain ostensibly discogenic in origin. These obstacles are considerable; however, recent research has begun to shed light on possible breakthrough technologies. Such breakthroughs include revolutionary imaging to better identify tissue sources of pain. Furthermore, novel molecular therapies have been shown to be able to mediate the progression of degenerative disc disease in some large animal studies, and even provide some insight into suppressing the development of tissue sources of discogenic pain. These potential breakthrough technologies have yet to be translated for clinical use.

Getting to the Core: Exploring the Embryonic Development from Notochord to Nucleus Pulposus

The intervertebral disc (IVD) is the largest avascular organ of the human body and plays a fundamental role in providing the spine with its unique structural and biomechanical functions. The inner part of the IVD contains the nucleus pulposus (NP), a gel-like tissue characterized by a high content of type II collagen and proteoglycans, which is crucial for the disc's load-bearing and shock-absorbing properties. With aging and IVD degeneration (IDD), the NP gradually loses its physiological characteristics, leading to low back pain and additional sequelae. In contrast to surrounding spinal tissues, the NP presents a distinctive embryonic development since it directly derives from the notochord. This review aims to explore the embryology of the NP, emphasizing the pivotal roles of key transcription factors, which guide the differentiation and maintenance of the NP cellular components from the notochord and surrounding sclerotome. Through an understanding of NP development, we sought to investigate the implications of the critical developmental aspects in IVD-related pathologies, such as IDD and the rare malignant chordomas. Moreover, this review discusses the therapeutic strategies targeting these pathways, including the novel regenerative approaches leveraging insights from NP development and embryology to potentially guide future treatments.

Notochordal cells: A potential therapeutic option for intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a prevalent musculoskeletal degenerative disorder worldwide, and ~40% of chronic low back pain cases are associated with IDD. Although the pathogenesis of IDD remains unclear, the reduction in nucleus pulposus cells (NPCs) and degradation of the extracellular matrix (ECM) are critical factors contributing to IDD. Notochordal cells (NCs), derived from the notochord, which rapidly degrades after birth and is eventually replaced by NPCs, play a crucial role in maintaining ECM homeostasis and preventing NPCs apoptosis. Current treatments for IDD only provide symptomatic relief, while lacking the ability to inhibit or reverse its progression. However, NCs and their secretions possess anti-inflammatory properties and promote NPCs proliferation, leading to ECM formation. Therefore, in recent years, NCs therapy targeting the underlying cause of IDD has emerged as a novel treatment strategy. This article provides a comprehensive review of the latest research progress on NCs for IDD, covering their biological characteristics, specific markers, possible mechanisms involved in IDD and therapeutic effects. It also highlights significant future directions in this field to facilitate further exploration of the pathogenesis of IDD and the development of new therapies based on NCs strategies.

Semi-synthetic degradable notochordal cell-derived matrix hydrogel for use in degenerated intervertebral discs: Initial in vitro characterization

Low back pain is the leading cause of disability worldwide, but current therapeutic interventions are palliative or surgical in nature. Loss of notochordal cells (NCs) and degradation of the healthy matrix in the nucleus pulposus (NP), the central tissue of intervertebral discs (IVDs), has been associated with onset of degenerative disc changes. Recently, we established a protocol for decellularization of notochordal cell derived matrix (NCM) and found that it can provide regenerative cues to nucleus pulposus cells of the IVD. Here, we combined the biologically regenerative properties of decellularized NCM with the mechanical tunability of a poly(ethylene glycol) hydrogel to additionally address biomechanics in the degenerate IVD. We further introduced a hydrolysable PEG-diurethane crosslinker for slow degradation of the gels in vivo. The resulting hydrogels were tunable over a broad range of stiffness's (0.2 to 4.5 kPa), matching that of NC-rich and -poor NP tissues, respectively. Gels formed within 30 min, giving ample time for handling, and remained shear-thinning post-polymerization. Gels also slowly released dNCM over 28 days as measured by GAG effusion. Viability of encapsulated bone marrow stromal cells after extrusion through a needle remained high. Although encapsulated NCs stayed viable over two weeks, their metabolic activity decreased, and their phenotype was lost in physiological medium conditions in vitro. Overall, the obtained gels hold promise for application in degenerated IVDs but require further tuning for combined use with NCs.

Hydrogel-Loaded Exosomes: A Promising Therapeutic Strategy for Musculoskeletal Disorders

Clinical treatment strategies for musculoskeletal disorders have been a hot research topic. Accumulating evidence suggests that hydrogels loaded with MSC-derived EVs show great potential in improving musculoskeletal injuries. The ideal hydrogels should be capable of promoting the development of new tissues and simulating the characteristics of target tissues, with the properties matching the cell-matrix constituents of autologous tissues. Although there have been numerous reports of hydrogels loaded with MSC-derived EVs for the repair of musculoskeletal injuries, such as intervertebral disc injury, tendinopathy, bone fractures, and cartilage injuries, there are still many hurdles to overcome before the clinical application of modified hydrogels. In this review, we focus on the advantages of the isolation technique of EVs in combination with different types of hydrogels. In this context, the efficacy of hydrogels loaded with MSC-derived EVs in different musculoskeletal injuries is discussed in detail to provide a reference for the future application of hydrogels loaded with MSC-derived EVs in the clinical treatment of musculoskeletal injuries.

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

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

An insight on the N-glycome of notochordal cell-rich porcine nucleus pulposus during maturation

Degeneration of the intervertebral disc is an age-related condition. It also accompanies the disappearance of the notochordal cells, which are remnants of the developmental stages of the nucleus pulposus (NP). Molecular changes such as extracellular matrix catabolism, cellular phenotype, and glycosaminoglycan loss in the NP have been extensively studied. However, as one of the most significant co- and posttranslational modifications, glycosylation has been overlooked in cells in degeneration. Here, we aim to characterize the N-glycome of young and mature NP and identify patterns related to aging. Accordingly, we isolated N-glycans from notochordal cell-rich NP from porcine discs, characterized them using a combined approach of exoglycosidase digestions and analysis with hydrophilic interaction ultra-performance liquid chromatography and mass spectrometry. We have assigned over 300 individual N-glycans for each age group. Moreover, we observed a notable abundance of antennary structures, galactosylation, fucosylation, and sialylation in both age groups. In addition, as indicated from our results, increasing outer arm fucosylation and decreasing α(2,3)-linked sialylation with aging suggest that these traits are age-dependent. Lastly, we have focused on an extensive characterization of the N-glycome of the notochordal cell-rich NP in aging without inferred degeneration, describing glycosylation changes specific for aging only. Our findings in combination with those of other studies, suggest that the degeneration of the NP does not involve identical processes as aging.

A bovine nucleus pulposus explant culture model

Low back pain is a global health problem that is frequently caused by intervertebral disc degeneration (IVDD). Sulfated glycosaminoglycans (sGAGs) give the healthy nucleus pulposus (NP) a high fixed charge density (FCD), which creates an osmotic pressure that enables the disc to withstand high compressive forces. However, during IVDD sGAG reduction in the NP compromises biomechanical function. The aim of this study was to develop an ex vivo NP explant model with reduced sGAG content and subsequently investigate biomechanical restoration via injection of proteoglycan-containing notochordal cell-derived matrix (NCM). Bovine coccygeal NP explants were cultured in a bioreactor chamber and sGAG loss was induced by chondroitinase ABC (chABC) and cultured for up to 14 days. Afterwards, diurnal loading was studied, and explant restoration was investigated via injection of NCM. Explants were analyzed via histology, biochemistry, and biomechanical testing via stress relaxation tests and height measurements. ChABC injection induced dose-dependent sGAG reduction on Day 3, however, no dosing effects were detected after 7 and 14 days. Diurnal loading reduced sGAG loss after injection of chABC. NCM did not show an instant biomechanical (equilibrium pressure) or biochemical (FCD) restoration, as the injected fixed charges leached into the medium, however, NCM stimulated proliferation and increased Alcian blue staining intensity and matrix organization. NCM has biological repair potential and biomaterial/NCM combinations, which could better entrap NCM within the NP tissue, should be investigated in future studies. Concluding, chABC induced progressive, time-, dose- and loading-dependent sGAG reduction that led to a loss of biomechanical function. Keywords biomechanics | intervertebral disc | matrix degradation | low back pain | proteoglycans.

Detergent-Free Decellularization of Notochordal Cell-Derived Matrix Yields a Regenerative, Injectable, and Swellable Biomaterial

Porcine notochordal cell-derived matrix (NCM) has anti-inflammatory and regenerative effects on degenerated intervertebral discs. For its clinical use, safety must be assured. The porcine DNA is concerning because of (1) the transmission of endogenous retroviruses and (2) the inflammatory potential of cell-free DNA. Here, we present a simple, detergent-free protocol: tissue lyophilization lyses cells, and matrix integrity is preserved by limiting swelling during decellularization. DNA is digested quickly by a high nuclease concentration, followed by a short washout. Ninety-four percent of DNA was removed, and there was no loss of glycosaminoglycans or collagen. Forty-three percent of the total proteins remained in the decellularized NCM (dNCM). dNCM stimulated as much GAG production as NCM in nucleus pulposus cells but lost some anti-inflammatory effects. Reconstituted pulverized dNCM yielded a soft, shear-thinning biomaterial with a swelling ratio of 350% that also acted as an injectable cell carrier (cell viability >70%). dNCM can therefore be used as the basis for future biomaterials aimed at disc regeneration on a biological level and may restore joint mechanics by creating swelling pressure within the intervertebral disc.

Intervertebral Disc Degeneration: Biomaterials and Tissue Engineering Strategies toward Precision Medicine

Intervertebral disc degeneration is a common cause of discogenic low back pain resulting in significant disability. Current conservative or surgical intervention treatments do not reverse the underlying disc degeneration or regenerate the disc. Biomaterial-based tissue engineering strategies exhibit the potential to regenerate the disc due to their capacity to modulate local tissue responses, maintain the disc phenotype, attain biochemical homeostasis, promote anatomical tissue repair, and provide functional mechanical support. Despite preliminary positive results in preclinical models, these approaches have limited success in clinical trials as they fail to address discogenic pain. This review gives insights into the understanding of intervertebral disc pathology, the emerging concept of precision medicine, and the rationale of personalized biomaterial-based tissue engineering tailored to the severity of the disease targeting early, mild, or severe degeneration, thereby enhancing the efficacy of the treatment for disc regeneration and ultimately to alleviate discogenic pain. Further research is required to assess the relationship between disc degeneration and lower back pain for developing future clinically relevant therapeutic interventions targeted towards the subgroup of degenerative disc disease patients.

Notochordal Cell-Based Treatment Strategies and Their Potential in Intervertebral Disc Regeneration

Chronic low back pain is the number one cause of years lived with disability. In about 40% of patients, chronic lower back pain is related to intervertebral disc (IVD) degeneration. The standard-of-care focuses on symptomatic relief, while surgery is the last resort. Emerging therapeutic strategies target the underlying cause of IVD degeneration and increasingly focus on the relatively overlooked notochordal cells (NCs). NCs are derived from the notochord and once the notochord regresses they remain in the core of the developing IVD, the nucleus pulposus. The large vacuolated NCs rapidly decline after birth and are replaced by the smaller nucleus pulposus cells with maturation, ageing, and degeneration. Here, we provide an update on the journey of NCs and discuss the cell markers and tools that can be used to study their fate and regenerative capacity. We review the therapeutic potential of NCs for the treatment of IVD-related lower back pain and outline important future directions in this area. Promising studies indicate that NCs and their secretome exerts regenerative effects, via increased proliferation, extracellular matrix production, and anti-inflammatory effects. Reports on NC-like cells derived from embryonic- or induced pluripotent-stem cells claim to have successfully generated NC-like cells but did not compare them with native NCs for phenotypic markers or in terms of their regenerative capacity. Altogether, this is an emerging and active field of research with exciting possibilities. NC-based studies demonstrate that cues from developmental biology can pave the path for future clinical therapies focused on regenerating the diseased IVD.

Current Status of the Instructional Cues Provided by Notochordal Cells in Novel Disc Repair Strategies

Numerous publications over the past 22 years, beginning with a seminal paper by Aguiar et al., have demonstrated the ability of notochordal cell-secreted factors to confer anabolic effects upon intervertebral disc (IVD) cells. Since this seminal paper, other scientific publications have demonstrated that notochordal cells secrete soluble factors that can induce anti-inflammatory, pro-anabolic and anti-cell death effects upon IVD nucleus pulposus (NP) cells in vitro and in vivo, direct human bone marrow-derived mesenchymal stem cells toward an IVD NP-like phenotype and repel neurite ingrowth. More recently these factors have been characterized, identified, and used therapeutically to induce repair upon injured IVDs in small and large pre-clinical animal models. Further, notochordal cell-rich IVD NPs maintain a stable, healthy extracellular matrix whereas notochordal cell-deficient IVDs result in a biomechanically and extracellular matrix defective phenotype. Collectively this accumulating body of evidence indicates that the notochordal cell, the cellular originator of the intervertebral disc holds vital instructional cues to establish, maintain and possibly regenerate the intervertebral disc.

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.

Injectable exosome-functionalized extracellular matrix hydrogel for metabolism balance and pyroptosis regulation in intervertebral disc degeneration

Exosome therapy is a promising therapeutic approach for intervertebral disc degeneration (IVDD) and achieves its therapeutic effects by regulating metabolic disorders, the microenvironment and cell homeostasis with the sustained release of microRNAs, proteins, and transcription factors. However, the rapid clearance and disruption of exosomes are the two major challenges for the application of exosome therapy in IVDD. Herein, a thermosensitive acellular extracellular matrix (ECM) hydrogel coupled with adipose-derived mesenchymal stem cell (ADSC) exosomes (dECM@exo) that inherits the superior properties of nucleus pulposus tissue and ADSCs was fabricated to ameliorate IVDD. This thermosensitive dECM@exo hydrogel system can provide not only in situ gelation to replenish ECM leakage in nucleus pulposus cells (NPCs) but also an environment for the growth of NPCs. In addition, sustained release of ADSC-derived exosomes from this system regulates matrix synthesis and degradation by regulating matrix metalloproteinases (MMPs) and inhibits pyroptosis by mitigating the inflammatory response in vitro. Animal results demonstrated that the dECM@exo hydrogel system maintained early IVD microenvironment homeostasis and ameliorated IVDD. This functional system can serve as a powerful platform for IVD drug delivery and biotherapy and an alternative therapy for IVDD.

Mitochondrial quality control in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common and early-onset pathogenesis in the human lifespan that can increase the risk of low back pain. More clarification of the molecular mechanisms associated with the onset and progression of IDD is likely to help establish novel preventive and therapeutic strategies. Recently, mitochondria have been increasingly recognized as participants in regulating glycolytic metabolism, which has historically been regarded as the main metabolic pathway in intervertebral discs due to their avascular properties. Indeed, mitochondrial structural and functional disruption has been observed in degenerated nucleus pulposus (NP) cells and intervertebral discs. Multilevel and well-orchestrated strategies, namely, mitochondrial quality control (MQC), are involved in the maintenance of mitochondrial integrity, mitochondrial proteostasis, the mitochondrial antioxidant system, mitochondrial dynamics, mitophagy, and mitochondrial biogenesis. Here, we address the key evidence and current knowledge of the role of mitochondrial function in the IDD process and consider how MQC strategies contribute to the protective and detrimental properties of mitochondria in NP cell function. The relevant potential therapeutic treatments targeting MQC for IDD intervention are also summarized. Further clarification of the functional and synergistic mechanisms among MQC mechanisms may provide useful clues for use in developing novel IDD treatments.

Selective Retention of Bone Marrow Stromal Cells with Gelatin Sponge for Repair of Intervertebral Disc Defects after Microendoscopic Discectomy: A Prospective Controlled Study and 2-Year Follow-Up

Objective

Discectomy remains the classic procedure for treating lumbar intervertebral disc (IVD) herniation, but the occurrence of defects after discectomy is thought to be an important cause generating recurrent and accelerated IVD degeneration. Previous studies attempted suture of the annulus fissure, but the validity of this technique on restraining the degenerative process is controversial. On the other hand, cell therapies have been shown in multiple clinical and basic studies. Our purpose was to investigate the effectiveness of selective retention of autologous Bone Marrow Stromal Cells (BMSCs) with gelatin sponge in combination with annulus fibrosus suture (AFS) for the repair of IVD defects following mobile microendoscopic discectomy (MMED).

Methods

This prospective, two-armed, and controlled clinical study was conducted from December 2016 to December 2018. Written informed consent was obtained from each patient. Forty-five patients with typical symptoms, positive signs of radiculopathy, and obvious lumbar disc herniation observed by MRI were enrolled. Patients were divided into 3 groups with different treating methods: MMED (n = 15), MMED+AFS (n = 15), and MMED+AFS+BMSCs (n = 15). A postoperative 2-year follow-up was performed to evaluate the patient-reported outcomes of VAS, ODI, and SF-36. The improvement rate of VAS and ODI was calculated as [(latest‐preoperative)/preoperative] to evaluate the therapeutic effect of the three groups. Assessment parameters included Pfirrmann grade, intervertebral disc height (IDH), and disc protrusion size (DPS), as measured by MRI to evaluate the morphological changes.

Results

All patients enrolled had a postoperative follow-up at 3, 6, 12, and 24 months. VAS and ODI scores were significantly improved compared to the preoperative status in all three groups with a mean DPS reduction rate over 50%. At the final follow-up, the improvement rate of the VAS score in the MMED+AFS+BMSCs group was significantly higher than the MMED+AFS and MMED groups (80.1% ± 7.6% vs. 71.3% ± 7.0% vs. 70.1% ± 7.8%), while ODI improvement showed a significant change (65.6% ± 8.8% vs. 59.9% ± 5.5% vs. 57.8% ± 8.1%). All participants showed significant improvement in SF-36 PCS and MCS; the differences between each group were not significant. The mean IDH loss rate of the MMED+AFS+BMSCs group was also significantly lower than other groups (−17.2% ± 1.3% vs. −27.6% ± 0.7% vs. −29.3% ± 2.2%). The Pfirrmann grade was aggravated in the MMED and MMED+AFS groups while maintained at the preoperative grade in the MMED+AFS+BMSCs group. No adverse events of cell transplantation or recurrence were found in all patients during the postoperative follow-up period.

Conclusions

It is feasible and effective to repair lumbar IVD defects using SCR-enriched BMSCs with gelatin sponges, which warrants further study and development as a cell-based therapy for IVD repair.

Uncovering molecular targets for regenerative therapy in degenerative disc disease: do small leucine-rich proteoglycans hold the key?

BACKGROUND CONTEXT

Small leucine-rich proteoglycans (SLRPs) play an essential role in extracellular matrix (ECM) organization and function. Recently, dysregulation of SLRPs has been implicated in degenerative disc disease (DDD). An in-depth analysis using high-throughput proteomic sequencing might provide valuable information on their implications in health and disease.

PURPOSE

To utilize proteomics for analyzing the expression of SLRPs in fetal, healthy adult, and degenerated discs, to identify possible molecular targets to halt or reverse the degenerative process.

STUDY DESIGN

Experimental analysis.

METHODS

Proteomic signatures of 8 magnetic resonance imaging (MRI) normal lumbar discs (ND) [harvested from brain dead alive organ donors] were compared to 8 fetal disc samples (FD) [harvested from fetal spines devoid of congenital anomalies following spontaneous or medical termination of pregnancy] and 8 degenerate discs (DD) [collected from patients undergoing fusion surgery]. The various functional pathways along with the differential expression of SLRPs and the associated changes in collagens, large proteoglycans (LLRPs), matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) have been analyzed further using bioinformatics. This project was self-funded by the Ganga Orthopedic Research and Education Foundation.

RESULTS

ESI-LC-MS/MS analysis revealed a total of 1,029 proteins in FD, 1,785 proteins in ND, and 1,775 proteins in DD. Fetal disc proteins were engaged mainly in ribosomal pathways (indicating active proliferation and regenerative potential). The healthy adult discs (ND) primarily participated in ECM maintenance and basic metabolic pathways, whereas the unique proteins of DD group were involved in inflammatory (Complement and coagulation cascades, Systemic Lupus Erythematosus and Leukocyte transendothelial migration) pathways and infective (Staphylococcus aureus infection, Prion diseases, Amoebiasis, Pertussis, and Legionellosis) channels which favor the recent concepts of inflammaging and subclinical infection as causes of DDD. Analysis of SLRPs revealed the upregulation of Biglycan in FDs and downregulation of Lumican, Decorin, Prolargin, and Chondroadherin in the DD group. The universal decrease in the abundance of SLRPs in the DD group was associated with an increase in MMPs and a reduction in TIMPs, collagen and LLRP content.

CONCLUSIONS

Our study documents the influence of SLRPs in the maintenance of disc health and also the need for future research in using them for disc regeneration.

CLINICAL SIGNIFICANCE

The various SLRPs that we identified are all known to have a beneficial influence on ECM integrity and a negative effect on the degenerative process at different stages in the evolution of degeneration. Biglycan, which is abundantly present in a fetus, may be suitable for regenerative therapy, and the other SLRPs like Lumican, Prolargin, Decorin, and Chondroadherin may serve the same purpose and/or as biomarkers.

Human iPSCs can be differentiated into notochordal cells that reduce intervertebral disc degeneration in a porcine model

Introduction: As many as 80% of the adult population experience back pain at some point in their lifetimes. Previous studies have indicated a link between back pain and intervertebral disc (IVD) degeneration. Despite decades of research, there is an urgent need for robust stem cell therapy targeting underlying causes rather than symptoms. It has been proposed that notochordal cells (NCs) appear to be the ideal cell type to regenerate the IVD: these cells disappear in humans as they mature, are replaced by nucleus pulposus (NP) cells, and their disappearance correlates with the initiation of degeneration of the disc. Human NCs are in short supply, thus here aimed for generation of notochordal-like cells from induced pluripotent cells (iPSCs). Methods: Human iPSCs were generated from normal dermal fibroblasts by transfecting plasmids encoding for six factors: OCT4, SOX2, KLF4, L-MYC, LIN28, and p53 shRNA. Then the iPSCs were treated with GSK3i to induce differentiation towards Primitive Streak Mesoderm (PSM). The differentiation was confirmed by qRT-PCR and immunofluorescence. PSM cells were transfected with Brachyury (Br)-encoding plasmid and the cells were encapsulated in Tetronic-tetraacrylate-fibrinogen (TF) hydrogel that mimics the NP environment (G'=1kPa), cultured in hypoxic conditions (2% O2) and with specifically defined growth media. The cells were also tested in vivo in a large animal model. IVD degeneration was induced after an annular puncture in pigs, 4 weeks later the cells were injected and IVDs were analyzed at 12 weeks after the injury using MRI, gene expression analysis and histology. Results: After short-term exposure of iPSCs to GSK3i there was a significant change in cell morphology, Primitive Streak Mesoderm (PSM) markers (Brachyury, MIXL1, FOXF1) were upregulated and markers of pluripotency (Nanog, Oct4, Sox2) were downregulated, both compared to the control group. PSM cells nucleofected with Br (PSM-Br) cultured in TF hydrogels retained the NC phenotype consistently for up to 8 weeks, as seen in the gene expression analysis. PSM-Br cells were co-cultured with bone marrow (BM)-derived mesenchymal stem cells (MSCs) which, with time, expressed the NC markers in higher levels, however the levels of expression in BM-MSCs alone did not change. Higher expression of NC and NP marker genes in human BM-MSCs was found to be induced by iNC-condition media (iNC-CM) than porcine NC-CM. The annular puncture induced IVD degeneration as early as 2 weeks after the procedure. The injected iNCs were detected in the degenerated discs after 8 weeks in vivo. The iNC-treated discs were found protected from degeneration. This was evident in histological analysis and changes in the pH levels, indicative of degeneration state of the discs, observed using qCEST MRI. Immunofluorescence stains show that their phenotype was consistent with the in vitro study, namely they still expressed the notochordal markers Keratin 18, Keratin 19, Noto and Brachyury. Conclusion: In the present study, we report a stepwise differentiation method to generate notochordal cells from human iPSCs. These cells not only demonstrate a sustainable notochordal cell phenotype in vitro and in vivo, but also show the functionality of notochordal cells and have protective effect in case of induced disc degeneration and prevent the change in the pH level of the injected IVDs. The mechanism of this effect could be suggested via the paracrine effect on resident cells, as it was shown in the in vitro studies with MSCs.

Notochordal cell matrix: An inhibitor of neurite and blood vessel growth?

Blood vessel and neurite ingrowth into the degenerating intervertebral disc (IVD) are related to pain. In reported studies, notochordal cell (NC)-conditioned medium (NCCM) induced a regenerative response of nucleus pulposus (NP) cells, but also inhibition of neurite and vessel formation. NC matrix (NCM) derived from NC-rich NP tissue, induced even stronger anabolic effects than NCCM. Thus, the aim was to investigate whether NCM has similar anti-neurogenic and -angiogenic properties as NCCM. NCM and NCCM where produced from porcine NC-rich NP tissue. Human umbilical vein endothelial cells (HUVECs) were cultured in base medium (BM, 300 mOsm), NCCM (produced at 300 and 400 mOsm), NCM, or with chondroitin sulfate (CS, positive control) in angiogenesis-inducing medium, after which vessel length was measured. Although CS alone inhibited vessel growth, NCCM (both osmolarities) stimulated vessel formation by HUVECs. NCM did not affect vessel growth relative to BM. SH-SY5Y cells were cultured in BM, NCCM, and NCM on poly-D-lysine coated and polystyrene surfaces, and analyzed for neurite length and percentage of neurite expressing cells. On coated surfaces, neither NCCM nor NCM affected neurite growth. On a polystyrene surface, NCCM and NCM induced a higher number of neurite-expressing cells. NCCM's previously reported anti-angiogenic and -neurogenic effects were not observed in this study. Although addition of CS inhibited HUVEC vessel formation, other factors may be present in NCCM and NCM that affect neurite and vessel growth. Therefore, future studies testing an NC-based regenerative strategy should carefully assess the risk of such adverse effects in an in vivo setting. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. J Orthop Res 36:3188-3195, 2018.

Injectable decellularized nucleus pulposus-based cell delivery system for differentiation of adipose-derived stem cells and nucleus pulposus regeneration

Stem cell-based tissue engineering is a promising treatment for intervertebral disc (IVD) degeneration. A bio-scaffold that can maintain the function of transplanted cells and possesses favorable mechanical properties is needed in tissue engineering. Decellularized nucleus pulposus (dNP) has the potential to be a suitable bio-scaffold because it mimics the native nucleus pulposus (NP) composition. However, matrix loss during decellularization and difficulty in transplantation limit the clinical application of dNP scaffolds. In this study, we fabricated an injectable dNP-based cell delivery system (NPCS) and evaluated its properties by assessing the microstructure, biochemical composition, water content, biosafety, biostability, and mechanical properties. We also investigated the stimulatory effects of the bio-scaffold on the NP-like differentiation of adipose-derived stem cells (ADSCs) in vitro and the regenerative effects of the NPCS on degenerated NP in an in vivo animal model. The results showed that approximately 68% and 43% of the collagen and sGAG, respectively, remained in the NPCS after 30 days. The NPCS also showed mechanical properties similar to those of fresh NP. In addition, the NPCS was biocompatible and able to induce NP-like differentiation and extracellular matrix (ECM) synthesis in ADSCs. The disc height index (almost 81%) and the MRI index (349.05 ± 38.48) of the NPCS-treated NP were significantly higher than those of the degenerated NP after 16 weeks. The NPCS also partly restored the ECM content and the structure of degenerated NP in vivo. Our NPCS has good biological and mechanical properties and has the ability to promote the regeneration of degenerated NP. STATEMENT OF SIGNIFICANCE: Nucleus pulposus (NP) degeneration is usually the origin of intervertebral disc degeneration. Stem cell-based tissue engineering is a promising treatment for NP regeneration. Bio-scaffolds which have favorable biological and mechanical properties are needed in tissue engineering. Decellularized NP (dNP) scaffold is a potential choice for tissue engineering, but the difficulty in balancing complete decellularization and retaining ECM limits its usage. Instead of choosing different decellularization protocols, we complementing the sGAG lost during decellularization by cross-linking via genipin and fabricating an injectable dNP-based cell delivery system (NPCS) which has similar components as the native NP. We also investigated the biological and mechanical properties of the NPCS in vitro and verified its regenerative effects on degenerated IVDs in an animal model.

Critical aspects and challenges for intervertebral disc repair and regeneration-Harnessing advances in tissue engineering

Low back pain represents the highest burden of musculoskeletal diseases worldwide and intervertebral disc degeneration is frequently associated with this painful condition. Even though it remains challenging to clearly recognize generators of discogenic pain, tissue regeneration has been accepted as an effective treatment option with significant potential. Tissue engineering and regenerative medicine offer a plethora of exploratory pathways for functional repair or prevention of tissue breakdown. However, the intervertebral disc has extraordinary biological and mechanical demands that must be met to assure sustained success. This concise perspective review highlights the role of the disc microenvironment, mechanical and clinical design considerations, function vs mimicry in biomaterial‐based and cell engineering strategies, and potential constraints for clinical translation of regenerative therapies for the intervertebral disc.

Notochordal cell matrix as a bioactive lubricant for the osteoarthritic joint

Notochordal cell derived matrix (NCM) can induce regenerative effects on nucleus pulposus cells and may exert such effects on chondrocytes as well. Furthermore, when dissolved at low concentrations, NCM forms a viscous fluid with potential lubricating properties. Therefore, this study tests the feasibility of the use of NCM as a regenerative lubricant for the osteoarthritic joint. Chondrocyte-seeded alginate beads were cultured in base medium (BM), BM with NCM (NCM), or BM with TGF-β1 (TGF), as well as BM and NCM treated with IL-1β. NCM increased GAG deposition and cell proliferation (stronger than TGF), and GAG/DNA ratio and hydroxyproline content (similar to TGF). These effects were maintained in the presence of IL-1β. Moreover, NCM mitigated expression of IL-1β-induced IL-6, IL-8, ADAMTS-5 and MMP-13. Reciprocating sliding friction tests of cartilage on glass were performed to test NCM's lubricating properties relative to hyaluronic acid (HA), and showed a dose-dependent reduction in coefficient of friction with NCM, similar to HA. NCM has anabolic and anti-inflammatory effects on chondrocytes, as well as lubricating properties. Therefore, intra-articular NCM injection may have potential as a treatment to minimize pain while restoring the affected cartilage tissue in the osteoarthritic joint.