Therapeutic potential of growth differentiation factors in the treatment of degenerative disc diseases

Comparison of the efficacy of autologous Lp-PRP and Lr-PRP for treating intervertebral disc degeneration: in vitro and in vivo study

BACKGROUND

Intervertebral disc degeneration (IDD) was the most common cause of low back pain. Platelet rich plasma (PRP) has the potential to repair IDD, however, there is still no conclusion on whether Leukocyte-poor platelet rich plasma (Lp-PRP) or Leukocyte-rich platelet rich plasma (Lr-PRP) is better for the treatment of IDD.

METHODS

First, we conducted an in vitro study to compare the effects of autologous Lp-PRP and Lr-PRP on human degenerated nucleus pulposus (NP) cells. Then we verified the in vivo effects of autologous Lp-PRP and Lr-PRP in treating disc degeneration through a rabbit IDD model.

RESULTS

The in vitro study showed both autologous Lp-PRP and Lr-PRP can promote the cell proliferation, the synthesis of COL II and Aggrecan of human degenerated NP cells, while Lp-PRP are better than Lr-PRP (P<0.05). In addition, only Lp-PRP can inhibit the apoptosis of human degenerated NP cells (P<0.05), whereas Lr-PRP activates the catabolism on the contrary (P<0.05). Further, the in vivo study through the rabbit IDD model verified that autologous Lp-PRP has better effects than autologous Lr-PRP in repairing IDD according to X-ray, MRI, histological, and immunohistochemical assessment (P<0.05, respectively). And the caspase-3 IHC results also showed that only autologous Lp-PRP treatment could inhibit apoptosis of NP cells in the rabbit IDD model (P<0.05).

CONCLUSION

Combining in vivo and in vitro studies, the present study confirmed that autologous Lp-PRP has a better effect than autologous Lr-PRP in repairing IDD, which may be due to the inflammatory factors (TNFα, IL-1β, etc.) in Lr-PRP antagonizing part of the repair effects and promoting the catabolism additionally. Therefore, our findings suggest that Lp-PRP may provide better results than Lr-PRP for treating IDD. Further randomized clinical trials will provide evidence to guide practice.

In silico modeling the potential clinical effect of growth factor treatment on the metabolism of human nucleus pulposus cells

Background

While growth factors have the potential to halt degeneration and decrease inflammation in animal models, the literature investigating the effect of dosage on human cells is lacking. Moreover, despite the completion of clinical trials using growth differentiation factor-5 (GDF-5), no results have been publicly released.

Aims

The overall objective was to quantitatively assess the effect of three clinically relevant concentrations of GDF-5 (0.25, 1, and 2 mg) as a therapeutic for disc regeneration.

Materials and methods

Firstly, this work experimentally determined the effects of GDF-5 concentration on the metabolic and matrix synthesis rates of human nucleus pulposus (NP) cells. Secondly, in silico modeling was employed to predict the subsequent regenerative effect of different GDF-5 treatments (± cells).

Results

This study suggests a trend of increased matrix synthesis with 0.25 and 1 mg of GDF-5. However, 2 mg of GDF-5 significantly upregulates oxygen consumption. Despite this, in silico models highlight the potential of growth factors in promoting matrix synthesis compared to cell-only treatments, without significantly perturbing the nutrient microenvironment.

Discussion

This work elucidates the potential of GDF-5 on human NP cells. Although the results did not reveal statistical differences across all doses, the variability and response among donors is an interesting finding. It highlights the complexity of human response to biological treatments and reinforces the need for further human research and personalized approaches. Furthermore, this study raises a crucial question about whether these potential biologics are more regenerative in nature or better suited as prophylactic therapies for younger patient groups.

Conclusion

Biological agents exhibit unique characteristics and features, demanding tailored development strategies and individualized assessments rather than a one-size-fits-all approach. Therefore, the journey to realizing the full potential of biological therapies is long and costly. Nonetheless, it holds the promise of revolutionizing spinal healthcare and improving the quality of life for patients suffering from discogenic back pain.

Regenerative therapy in geriatric patients with low back pain

Low back pain (LBP) is a prevalent and debilitating condition, particularly among older adults, with degenerative spinal disease being a major contributor. Regenerative therapy, which aims to repair and regenerate damaged spinal structures, has shown promise in providing long-term pain relief and functional improvement. This review focuses on the application and efficacy of regenerative therapies such as mesenchymal stem cells, platelet-rich plasma, and atelocollagen in older patients with LBP. Despite the potential benefits, there is a notable scarcity of studies specifically targeting the older population, and those available often have small sample sizes and limited age-related analyses. Our findings underscore the need for more comprehensive and well-designed clinical trials to evaluate the effectiveness of these therapies in older patients. Future research should prioritize larger age-specific studies to establish regenerative therapy as a viable and effective treatment option for LBP in the aging population.

A comprehensive review of cell transplantation and platelet-rich plasma therapy for the treatment of disc degeneration-related back and neck pain: A systematic evidence-based analysis

Low back pain (LBP) and neck pain predominate as the primary causes of disability. Cell- and platelet-rich plasma (PRP) products are potential therapies with clinical trials and reviews promoting their efficacy. Nonetheless, they frequently disregard the clinical significance of reported improvements. In this systematic review, the effectuated improvements in pain, disability, quality of life (QoL), and radiographic images are comprehensively described and scored on their clinical significance. An electronic database literature search was conducted on July 2023 for in-human assessment of cell or PRP products to alleviate discogenic pain. Papers were screened on quantitative pain, disability, QoL, radiographic improvements, and safety outcomes. Risk of bias was assessed through MINORS and Cochrane Source of Bias tools. Reported outcomes were obtained, calculated, and assessed to meet minimal clinically important difference (MCID) standards. From 7623 screened papers, a total of 80 articles met the eligibility criteria, presenting 68 specific studies. These presented at least 1974 treated patients. Overall, cell/PRP injections could alleviate pain and disability, resulting in MCID for pain and disability in up to a 2-year follow-up, similar to those observed in patients undergoing spinal fusion. Included trials predominantly presented high levels of bias, involved heterogeneous study designs, and only a minimal number of randomized controlled trials. Nonetheless, a clear clinically significant impact was observed for cell- and PRP-treated cohorts with overall good safety profiles. These results highlight a strong therapeutic potential but also underline the need for future cost-effectiveness assessments to determine the benefits of cell/PRP treatments.

Viscoelastic hydrogels regulate adipose-derived mesenchymal stem cells for nucleus pulposus regeneration

Low back pain is a leading cause of disability worldwide, often attributed to intervertebral disc (IVD) degeneration with loss of the functional nucleus pulposus (NP). Regenerative strategies utilizing biomaterials and stem cells are promising for NP repair. Human NP tissue is highly viscoelastic, relaxing stress rapidly under deformation. However, the impact of tissue-specific viscoelasticity on the activities of adipose-derived stem cells (ASC) remains largely unexplored. Here, we investigated the role of matrix viscoelasticity in regulating ASC differentiation for IVD regeneration. Viscoelastic alginate hydrogels with stress relaxation time scales ranging from 100 s to 1000s were developed and used to culture human ASCs for 21 days. Our results demonstrated that the fast-relaxing hydrogel significantly enhanced ASCs long-term cell survival and NP-like extracellular matrix secretion of aggrecan and type-II collagen. Moreover, gene expression analysis revealed a substantial upregulation of the mechanosensitive ion channel marker TRPV4 and NP-specific markers such as SOX9, HIF-1α, KRT18, CDH2 and CD24 in ASCs cultured within the fast-relaxing hydrogel, compared to slower-relaxing hydrogels. These findings highlight the critical role of matrix viscoelasticity in regulating ASC behavior and suggest that viscoelasticity is a key parameter for novel biomaterials design to improve the efficacy of stem cell therapy for IVD regeneration. STATEMENT OF SIGNIFICANCE: Systematically characterized the influence of tissue-mimetic viscoelasticity on ASC. NP-mimetic hydrogels with tunable viscoelasticity and tissue-matched stiffness. Long-term survival and metabolic activity of ASCs are substantially improved in the fast-relaxing hydrogel. The fast-relaxing hydrogel allows higher rate of cell protrusions formation and matrix remodeling. ASC differentiation towards an NP-like cell phenotype is promoted in the fast-relaxing hydrogel, with more CD24 positive expression indicating NP committed cell fate. The expression of TRPV4, a molecular sensor of matrix viscoelasticity, is significantly enhanced in the fast-relaxing hydrogel, indicating ASC sensing matrix viscoelasticity during cell development. The NP-specific ECM secretion of ASC is considerably influenced by matrix viscoelasticity, where the deposition of aggrecan and type-II collagen are significantly enhanced in the fast-relaxing hydrogel.

Transcriptomic profiling reveals key early response genes during GDF6-mediated differentiation of human adipose-derived stem cells to nucleus pulposus cells

Background

Stem cell-based therapies show promise as a means of repairing the degenerate intervertebral disc, with growth factors often used alongside cells to help direct differentiation toward a nucleus pulposus (NP)-like phenotype. We previously demonstrated adipose-derived stem cell (ASC) differentiation with GDF6 as optimal for generating NP-like cells through evaluating end-stage differentiation parameters. Here we conducted a time-resolved transcriptomic characterization of ASCs response to GDF6 stimulation to understand the early drivers of differentiation to NP-like cells.

Methods

Human ASCs were treated with recombinant human GDF6 for 2, 6, and 12 h. RNA sequencing and detailed bioinformatic analysis were used to assess differential gene expression, gene ontology (GO), and transcription factor involvement during early differentiation. Quantitative polymerase chain reaction (qPCR) was used to validate RNA sequencing findings and inhibitors used to interrogate Smad and Erk signaling pathways, as well as identify primary and secondary response genes.

Results

The transcriptomic response of ASCs to GDF6 stimulation was time-resolved and highly structured, with "cell differentiation" "developmental processes," and "response to stimulus" identified as key biological process GO terms. The transcription factor ERG1 was identified as a key early response gene. Temporal cluster analysis of differentiation genes identified positive regulation NP cell differentiation, as well as inhibition of osteogenesis and adipogenesis. A role for Smad and Erk signaling in the regulation of GDF6-induced early gene expression response was observed and both primary and secondary response genes were identified.

Conclusions

This study identifies a multifactorial early gene response that contributes to lineage commitment, with the identification of a number of potentially useful early markers of differentiation of ASCs to NP cells. This detailed insight into the molecular processes in response to GDF6 stimulation of ASCs is important for the development of an efficient and efficacious cell-based therapy for intervertebral disc degeneration-associated back pain.

Transforming growth factor-beta superfamily regulates mesenchymal stem cell osteogenic differentiation: A microRNA linking

The ability to differentiate into cells of different lineages, such as bone cells, is the principal value of adult mesenchymal stem cells (MSCs), which can be used with the final aim of regenerating damaged tissue. Due to its potential use and importance in regenerative medicine and tissue engineering, several questions have been raised regarding the molecular mechanisms of MSC differentiation. As one of the crucial mediators in organism development, the transforming growth factor-beta (TGF-β) superfamily directs MSCs' commitment to selecting differentiation pathways. This review aims to give an overview of the current knowledge on the mechanisms of the TGF-β superfamily in MSCs bone differentiation, with additional insight into the mutual regulation of microRNAs and TGF-β in osteogenesis.

LSW-Net: Lightweight Deep Neural Network Based on Small-World properties for Spine MR Image Segmentation

BACKGROUND

Segmenting spinal tissues from MR images is important for automatic image analysis. Deep neural network-based segmentation methods are efficient, yet have high computational costs.

PURPOSE

To design a lightweight model based on small-world properties (LSW-Net) to segment spinal MR images, suitable for low-computing-power embedded devices.

STUDY TYPE

Retrospective.

POPULATION

A total of 386 subjects (2948 images) from two independent sources. Dataset I: 214 subjects/779 images, all for disk degeneration screening, 147 had disk degeneration, 52 had herniated disc. Dataset II: 172 subjects/2169 images, 142 patients with vertebral degeneration, 163 patients with disc degeneration. 70% images in each dataset for training, 20% for validation, and 10% for testing.

FIELD STRENGTH/SEQUENCE

T1- and T2-weighted turbo spin echo sequences at 3 T.

ASSESSMENT

Segmentation performance of LSW-Net was compared with four mainstream (including U-net and U-net++) and five lightweight models using five radiologists' manual segmentations (vertebrae, disks, spinal fluid) as reference standard. LSW-Net was also deployed on NVIDIA Jetson nano to compare the pixels number in segmented vertebrae and disks.

STATISTICAL TESTS

All models were evaluated with accuracy, precision, Dice similarity coefficient (DSC), and area under the receiver operating characteristic (AUC). Pixel numbers segmented by LSW-Net on the embedded device were compared with manual segmentation using paired t-tests, with P < 0.05 indicating significance.

RESULTS

LSW-Net had 98.5% fewer parameters than U-net but achieved similar accuracy in both datasets (dataset I: DSC 0.84 vs. 0.87, AUC 0.92 vs. 0.94; dataset II: DSC 0.82 vs. 0.82, AUC 0.88 vs. 0.88). LSW-Net showed no significant differences in pixel numbers for vertebrae (dataset I: 5893.49 vs. 5752.61, P = 0.21; dataset II: 5073.42 vs. 5137.12, P = 0.56) and disks (dataset I: 1513.07 vs. 1535.69, P = 0.42; dataset II: 1049.74 vs. 1087.88, P = 0.24) segmentation on an embedded device compared to manual segmentation.

DATA CONCLUSION

Proposed LSW-Net achieves high accuracy with fewer parameters than U-net and can be deployed on embedded device, facilitating wider application.

EVIDENCE LEVEL

2.

TECHNICAL EFFICACY

1.

Vanillin-based functionalization strategy to construct multifunctional microspheres for treating inflammation and regenerating intervertebral disc

Intervertebral disc degeneration (IVDD) is one of the main causes of low back pain. Although local delivery strategies using biomaterial carriers have shown potential for IVDD treatment, it remains challenging for intervention against multiple adverse contributors by a single delivery platform. In the present work, we propose a new functionalization strategy using vanillin, a natural molecule with anti-inflammatory and antioxidant properties, to develop multifunctional gelatin methacrylate (GelMA) microspheres for local delivery of transforming growth factor β3 (TGFβ3) toward IVDD treatment. In vitro, functionalized microspheres not only improved the release kinetics of TGFβ3 but also effectively inhibited inflammatory responses and promoted the secretion of extracellular matrix (ECM) in lipopolysaccharide-induced nucleus pulposus (NP) cells. In vivo, functionalized platform plays roles in alleviating inflammation and oxidative stress, preserving the water content of NP and disc height, and maintaining intact structure and biomechanical functions, thereby promoting the regeneration of IVD. High-throughput sequencing suggests that inhibition of the phosphatidylinositol 3-kinase (PI3K)-Akt signaling might be associated with their therapeutic effects. In summary, the vanillin-based functionalization strategy provides a novel and simple way for packaging multiple functions into a single delivery platform and holds promise for tissue regeneration beyond the IVD.

Investigation of the Mitigation of DMSO-Induced Cytotoxicity by Hyaluronic Acid following Cryopreservation of Human Nucleus Pulposus Cells

To develop an off-the-shelf therapeutic product for intervertebral disc (IVD) repair using nucleus pulposus cells (NPCs), it is beneficial to mitigate dimethyl sulfoxide (DMSO)-induced cytotoxicity caused by intracellular reactive oxygen species (ROS). Hyaluronic acid (HA) has been shown to protect chondrocytes against ROS. Therefore, we examined the potential of HA on mitigating DMSO-induced cytotoxicity for the enhancement of NPC therapy. Human NPC cryopreserved in DMSO solutions were thawed, mixed with equal amounts of EDTA-PBS (Group E) or HA (Group H), and incubated for 3-5 h. After incubation, DMSO was removed, and the cells were cultured for 5 days. Thereafter, we examined cell viability, cell proliferation rates, Tie2 positivity (a marker of NP progenitor cells), and the estimated numbers of Tie2 positive cells. Fluorescence intensity of DHE and MitoSOX staining, as indicators for oxidative stress, were evaluated by flow cytometry. Group H showed higher rates of cell proliferation and Tie2 expressing cells with a trend toward suppression of oxidative stress compared to Group E. Thus, HA treatment appears to suppress ROS induced by DMSO. These results highlight the ability of HA to maintain NPC functionalities, suggesting that mixing HA at the time of transplantation may be useful in the development of off-the-shelf NPC products.

Molecular Basic of Pharmacotherapy of Cytokine Imbalance as a Component of Intervertebral Disc Degeneration Treatment

Intervertebral disc degeneration (IDD) and associated conditions are an important problem in modern medicine. The onset of IDD may be in childhood and adolescence in patients with a genetic predisposition. With age, IDD progresses, leading to spondylosis, spondylarthrosis, herniated disc, spinal canal stenosis. One of the leading mechanisms in the development of IDD and chronic back pain is an imbalance between pro-inflammatory and anti-inflammatory cytokines. However, classical therapeutic strategies for correcting cytokine imbalance in IDD do not give the expected response in more than half of the cases. The purpose of this review is to update knowledge about new and promising therapeutic strategies based on the correction of the molecular mechanisms of cytokine imbalance in patients with IDD. This review demonstrates that knowledge of the molecular mechanisms of the imbalance between pro-inflammatory and anti-inflammatory cytokines may be a new key to finding more effective drugs for the treatment of IDD in the setting of acute and chronic inflammation.

Comprehensive narrative review on the analysis of outcomes from cell transplantation clinical trials for discogenic low back pain

Background

Intervertebral disc (IVD) degeneration is one of the primary causes of low back pain (LBP) and despite a prominent prevalence, present treatment options remain inadequate for a large portion of LBP patients. New developments in regenerative therapeutics offer potentially powerful medical tools to modify this pathology, with specific focus on (stem) cell transplantations. Multiple clinical trials have since reported overall beneficial outcomes favoring cell therapy. Nonetheless, the significance of these improvements is often not (clearly) discussed. As such, this narrative review aims to summarize the significance of the reported improvements from human clinical trials on IVD-targeted cell therapy.

Methods

Through a comprehensive narrative review we discuss the improvements in pain, disability, quality of life, and imaging modalities and reported adverse events following cell therapy for discogenic pain.

Results

Most clinical trials were able to report clear and significant improvements in pain and disability outcomes. Imaging and quality of life improvements however were not as clearly reported but did present some enhancements for a select number of patients. Finally, whether cell therapy can outperform placebo treatment remains intangible.

Conclusions

Our review highlights the clinical significance of observed trends in pain and disability improvement. Nevertheless, reporting quality was found unsatisfactory and large-scale randomized controlled studies remain small in number. Future studies and articles should put more emphasis on improvements in imaging modalities and compare outcomes to (placebo) control groups to fully elucidate the efficacy and safety of cellular therapeutics against LBP.

Homing of vertebral-delivered mesenchymal stromal cells for degenerative intervertebral discs repair - an in vivo proof-of-concept study

Introduction

Cell transplantation shows promising results for intervertebral disc (IVD) repair, however, contemporary strategies present concerns regarding needle puncture damage, cell retention, and straining the limited nutrient availability. Mesenchymal stromal cell (MSC) homing is a natural mechanism of long-distance cellular migration to sites of damage and regeneration. Previous ex vivo studies have confirmed the potential of MSC to migrate over the endplate and enhance IVD-matrix production. In this study, we aimed to exploit this mechanism to engender IVD repair in a rat disc degeneration model.

Methods

Female Sprague Dawley rats were subjected to coccygeal disc degeneration through nucleus pulposus (NP) aspiration. In part 1; MSC or saline was transplanted into the vertebrae neighboring healthy or degenerative IVD subjected to irradiation or left untouched, and the ability to maintain the IVD integrity for 2 and 4 weeks was assessed by disc height index (DHI) and histology. For part 2, ubiquitously GFP expressing MSC were transplanted either intradiscally or vertebrally, and regenerative outcomes were compared at days 1, 5, and 14 post-transplantation. Moreover, the homing potential from vertebrae to IVD of the GFP+ MSC was assessed through cryosection mediated immunohistochemistry.

Results

Part 1 of the study revealed significantly improved maintenance of DHI for IVD vertebrally receiving MSC. Moreover, histological observations revealed a trend of IVD integrity maintenance. Part 2 of the study highlighted the enhanced DHI and matrix integrity for discs receiving MSC vertebrally compared with intradiscal injection. Moreover, GFP rates highlighted MSC migration and integration in the IVD at similar rates as the intradiscally treated cohort.

Conclusion

Vertebrally transplanted MSC had a beneficial effect on the degenerative cascade in their neighboring IVD, and thus potentially present an alternative administration strategy. Further investigation will be needed to determine the long-term effects, elucidate the role of cellular homing versus paracrine signaling, and validate our observations on a large animal model.

Regenerative medicine for the treatment of chronic low back pain: a narrative review

Low back pain (LBP) is a common and important clinical problem. In addition to pain, patients are also affected by personal, social, and economic burdens. Intervertebral disc (IVD) degeneration is a common cause of LBP, further increasing the patient's morbidity and medical costs. The limitations of current treatment strategies for long-term pain relief mean that increasing attention has been paid to regenerative medicine. We carried out a narrative review to explore the roles of four types of regenerative medicine for treating LBP: marrow-derived stem cells, growth factors, platelet-rich plasma, and prolotherapy. Marrow-derived stem cells are regarded as an ideal cell source for IVD regeneration. Growth factors may stimulate the synthesis of extracellular matrix and attenuate or reverse the degenerative process in IVD, while platelet-rich plasma, which contains multiple growth factors, is thought to be a promising alternative therapy for IVD degeneration. Prolotherapy can initiate the body's inflammatory healing response to repair injured joints and connective tissues. This review summarizes the mechanisms, in vitro and in vivo studies, and clinical applications of these four types of regenerative medicine in patients with LBP.

A crucial exosome-related gene pair (AAMP and ABAT) is associated with inflammatory cells in intervertebral disc degeneration

Identification of exosome-related genes (ERGs) and competing endogenous RNAs (ceRNAs) associated with intervertebral disc degeneration (IDD) may improve its diagnosis and reveal its underlying mechanisms. We downloaded 49 samples from Gene Expression Omnibus and identified candidate ERGs using differentially expressed ERGs (De-ERGs), exosome-related gene pairs (ERGPs), and machine learning algorithms [least absolute shrinkage and selection operator (LASSO) and support vector machine (SVM)]. Immune cell-related ERGs were selected via immune-infiltration analysis, and clinical values were assessed using receiver operating characteristic curves. Based on the De-ERGs, a ceRNA network comprising 1,512 links and 330 nodes was constructed and primarily related to signal transduction pathways, apoptosis-related biological processes, and multiple kinase-related molecular functions. In total, two crucial De-ERGs [angio-associated migratory cell protein (AAMP) and 4-aminobutyrate aminotransferase (ABAT)] were screened from results in De-ERGs, ERGPs, LASSO, and SVM. Increased AAMP expression and decreased ABAT expression were positively and negatively correlated with CD8⁺ T cell infiltration, respectively. AAMP/ABAT was the only pair differentially expressed in IDD and correlated with CD8⁺ T cell infiltration. Furthermore, AAMP/ABAT displayed higher accuracy in predicting IDD than individual genes. These results demonstrated the ERGP AAMP/ABAT as a robust signature for identifying IDD and associated with increased CD8⁺ T cell infiltration, suggesting it as a promising IDD biomarker.

Decellularized matrix for repairing intervertebral disc degeneration: Fabrication methods, applications and animal models

Intervertebral disc degeneration (IDD)-induced low back pain significantly influences the quality of life, placing a burden on public health systems worldwide. Currently available therapeutic strategies, such as conservative or operative treatment, cannot effectively restore intervertebral disc (IVD) function. Decellularized matrix (DCM) is a tissue-engineered biomaterial fabricated using physical, chemical, and enzymatic technologies to eliminate cells and antigens. By contrast, the extracellular matrix (ECM), including collagen and glycosaminoglycans, which are well retained, have been extensively studied in IVD regeneration. DCM inherits the native architecture and specific-differentiation induction ability of IVD and has demonstrated effectiveness in IVD regeneration in vitro and in vivo. Moreover, significant improvements have been achieved in the preparation process, mechanistic insights, and application of DCM for IDD repair. Herein, we comprehensively summarize and provide an overview of the roles and applications of DCM for IDD repair based on the existing evidence to shed a novel light on the clinical treatment of IDD.

N-acetylcysteine attenuates oxidative stress-mediated cell viability loss induced by dimethyl sulfoxide in cryopreservation of human nucleus pulposus cells: A potential solution for mass production

Background

Cell therapy is considered a promising strategy for intervertebral disc (IVD) regeneration. However, cell products often require long-term cryopreservation, which compromises cell viability and potency, thus potentially hindering commercialization and off-the-shelf availability. Dimethyl sulfoxide (DMSO) is a commonly used cryoprotectant, however, DMSO is associated with cytotoxicity and cell viability loss. This study aimed to investigate the effects of DMSO on human nucleus pulposus cells (NPC) and the role of oxidative stress in DMSO-induced cytotoxicity. Furthermore, we examined the potential of antioxidant N-acetylcysteine (NAC) supplementation to mitigate the negative effects of DMSO.

Methods

NPC were exposed to various concentrations of DMSO with or without a freezing cycle. Cell viability, cell apoptosis and necrosis rates, intracellular reactive oxygen species (ROS) levels, and gene expression of major antioxidant enzymes were evaluated. In addition, NAC was added to cryopreservation medium containing 10% DMSO and its effects on ROS levels and cell viability were assessed.

Results

DMSO concentrations ≤1% for 24 h did not significantly affect the NPC viability, whereas exposure to 5 and 10% DMSO (most commonly used concentration) caused cell viability loss (loss of 57% and 68% respectively after 24 h) and cell death in a dose- and time-dependent manner. DMSO increased intracellular and mitochondrial ROS (1.9-fold and 3.6-fold respectively after 12 h exposure to 10% DMSO) and downregulated gene expression levels of antioxidant enzymes in a dose-dependent manner. Tempering ROS through NAC treatment significantly attenuated DMSO-induced oxidative stress and supported maintenance of cell viability.

Conclusions

This study demonstrated dose- and time-dependent cytotoxic effects of DMSO on human NPC. The addition of NAC to the cryopreservation medium ameliorated cell viability loss by reducing DMSO-induced oxidative stress in the freeze-thawing cycle. These findings may be useful for future clinical applications of whole cells and cellular products.

Intradiscal injection of human recombinant BMP-4 does not reverse intervertebral disc degeneration induced by nuclectomy in sheep

Background

Methods

Results

Conclusion

The Translational Potential of This Article

Intradiscal Autologous Platelet-Rich Plasma Injection for Discogenic Low Back Pain: A Clinical Trial

Background. Platelet-rich plasma (PRP) contains high concentrations of growth factors and cytokines and may promote healing and tissue formation and exert anti-inflammatory effects. PRP has been shown to improve intervertebral disc degeneration in vivo and in vitro. This study is aimed at evaluating the effectiveness of autologous PRP on discogenic low back pain (DLBP) at 48 weeks postinjection in patients who received a single intradiscal injection. Methods. All patients received a single intradiscal injection of PRP in a prospective trial. The pain scores, lumbar function, and adverse events were assessed at 1 week, 4 weeks, 8 weeks, 12 weeks, 24 weeks, and 48 weeks postinjection and compared to the preinjection values (0 weeks). Results. Data were analysed from 31 patients with a 94% follow-up rate. Compared to preinjection, pain and lumbar function were significantly improved, and there were significant differences ( $P<0.05$ ) over the 48-week follow-up. Twenty-two (71%) patients were classified as successes after the intradiscal injection of PRP. One patient received surgery at two weeks postinjection due to intervertebral discitis. Conclusions. Intradiscal injection of PRP can significantly relieve pain sensation and improve lumbar function in patients with DLBP over a 48-week follow-up period. Further randomized controlled clinical trials are needed to assess the effects of this injection therapy.

Exosomes and exosomal miRNAs: A new therapy for intervertebral disc degeneration

Low back pain has been found as a major cause of global disease burden and disability. Intervertebral disc degeneration is recognized as the vital factor causing low back pain. Intervertebral disc degeneration has a complex mechanism and cannot be avoided. Traditional strategies for the treatment of intervertebral disc degeneration cannot meet the needs of intervertebral disc regeneration, so novel treatment methods are urgently required. Exosomes refer to extracellular vesicles that can be released by most cells, and play major roles in intercellular material transport and information transmission. MicroRNAs have been identified as essential components in exosomes, which can be selectively ingested by exosomes and delivered to receptor cells for the regulation of the physiological activities and functions of receptor cells. Existing studies have progressively focused on the role of exosomes and exosomal microRNAs in the treatment of intervertebral disc degeneration. The focus on this paper is placed on the changes of microenvironment during intervertebral disc degeneration and the biogenesis and mechanism of action of exosomes and exosomal microRNAs. The research results and deficiencies of exosomes and exosomal microRNAs in the regulation of apoptosis, extracellular matrix homeostasis, inflammatory response, oxidative stress, and angiogenesis in intervertebral disc degeneration are primarily investigated. The aim of this paper is to identify the latest research results, potential applications and challenges of this emerging treatment strategy.

Intradiscal Therapies for Lumbar Degenerative Disk Disease

Discogenic low back pain is a common musculoskeletal complaint in patients presenting to orthopaedic surgeons. In addition to surgical options, there are several nonsurgical intradiscal treatments that have gained interest, ranging from biologic, nonbiologic, cell-based, and molecular therapies. However, there is limited evidence for many of these techniques, and some are still in the clinical trial stage. We describe a broad overview of these intradiscal therapies, the mechanism of action, and the evidence behind them.

Current Insights Into the Maintenance of Structure and Function of Intervertebral Disc: A Review of the Regulatory Role of Growth and Differentiation Factor-5

Intervertebral disc degeneration (IDD), characterized by conversion of genotypic and phenotypic, is a major etiology of low back pain and disability. In general, this process starts with alteration of metabolic homeostasis leading to ongoing inflammatory process, extracellular matrix degradation and fibrosis, diminished tissue hydration, and impaired structural and mechanical functionality. During the past decades, extensive studies have focused on elucidating the molecular mechanisms of degeneration and shed light on the protective roles of various factors that may have the ability to halt and even reverse the IDD. Mutations of GDF-5 are associated with several human and animal diseases that are characterized by skeletal deformity such as short digits and short limbs. Growth and differentiation factor-5 (GDF-5) has been shown to be a promise biological therapy for IDD. Substantial literature has revealed that GDF-5 can decelerate the progression of IDD on the molecular, cellular, and organ level by altering prolonged imbalance between anabolism and catabolism. GDF family members are the central signaling moleculars in homeostasis of IVD and upregulation of their gene promotes the expression of healthy nucleus pulposus (NP) cell marker genes. In addition, GDF signaling is able to induce mesenchymal stem cells (MSCs) to differentiate into NPCs and mobilize resident cell populations as chemotactic signals. This review will discuss the promising critical role of GDF-5 in maintenance of structure and function of IVDs, and its therapeutic role in IDD endogenous repair.

Deletion of ApoE Leads to Intervertebral Disc Degeneration via Aberrant Activation of Adipokines

STUDY DESIGN

Animal experiment: a mouse model of intervertebral disc (IVD) degeneration induced by deletion of apolipoprotein E (apoE).

OBJECTIVE

The aim of this study was to investigate the role and mechanism of apoE on the process of IVD degeneration.

SUMMARY OF BACKGROUND DATA

Abnormal lipid metabolism has been demonstrated to be closely related to IVD degeneration, a common chronic degenerative joint disease. ApoE, a component of apolipoproteins, plays a crucial role in lipid transportation and metabolic balance. But the relationship between apoE and IVD degeneration remains largely unknown.

METHODS

ApoE knockout (KO) mouse was employed to investigate the progressive disc degeneration. The changes of vertebral bone and intervertebral disc space were measured by micro-computed tomography (micro-CT). The histo-morphological changes of cartilage endplate (CEP) and underlying signals were tested using immunohistochemistry and immunofluorescence staining.

RESULTS

The deletion of apoE gene accelerated the lumbar spine degeneration. Compared with WT mice, apoE KO mice showed reduced IVD space and increased vertebral bone mass. The progressive CEP degeneration was further found with cartilage degradation and endplate sclerosis in apoE KO mice. The deletion of apoE stimulated abnormal CEP bone remodeling and activation of adipokines signals.

CONCLUSION

The deletion of apoE gene induced abnormal activation of adipokines signals, thus contribute to the CEP degeneration.

LEVEL OF EVIDENCE

N/A.

Suppression of Sost/Sclerostin and Dickkopf-1 Augment Intervertebral Disc Structure in Mice

Intervertebral disc (IVD) degeneration is a leading cause of low back pain, characterized by accelerated extracellular matrix breakdown and IVD height loss, but there is no approved pharmacological therapeutic. Deletion of Wnt ligand competitor Lrp5 induces IVD degeneration, suggesting that Wnt signaling is essential for IVD homeostasis. Therefore, the IVD may respond to neutralization of Wnt ligand competitors sost(gene)/sclerostin(protein) and/or dickkopf-1 (dkk1). Anti-sclerostin antibody (scl-Ab) is an FDA-approved bone therapeutic that activates Wnt signaling. We aimed to (i) determine if pharmacological neutralization of sclerostin, dkk1, or their combination would stimulate Wnt signaling and augment IVD structure and (ii) determine the prolonged adaptation of the IVD to global, persistent deletion of sost. Nine-week-old C57Bl/6J female mice (n = 6-7/group) were subcutaneously injected 2×/week for 5.5 weeks with scl-Ab (25 mg/kg), dkk1-Ab (25 mg/kg), 3:1 scl-Ab/dkk1-Ab (18.75:6.25 mg/kg), or vehicle (veh). Separately, IVD of sost KO and wild-type (WT) mice (n = 8/group) were harvested at 16 weeks of age. First, compared with vehicle, injection of scl-Ab, dkk1-Ab, and 3:1 scl-Ab/dkk1-Ab similarly increased lumbar IVD height and β-catenin gene expression. Despite these similarities, only injection of scl-Ab alone strengthened IVD mechanical properties and decreased heat shock protein gene expressions. Genetically and compared with WT, sost KO enlarged IVD height, increased proteoglycan staining, and imbibed IVD hydration. Notably, persistent deletion of sost was compensated by upregulation of dkk1, which consequently reduced the cell nuclear fraction for Wnt signaling co-transcription factor β-catenin in the IVD. Lastly, RNA-sequencing pathway analysis confirmed the compensatory suppression of Wnt signaling and revealed a reduction of cellular stress-related pathways. Together, suppression of sost/sclerostin or dkk1 each augmented IVD structure by stimulating Wnt signaling, but scl-Ab outperformed dkk1-Ab in strengthening the IVD. Ultimately, postmenopausal women prescribed scl-Ab injections to prevent vertebral fracture may also benefit from a restoration of IVD height and health. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Protective Effects of Growth Differentiation Factor-6 on the Intervertebral Disc: An In Vitro and In Vivo Study

Growth differentiation factors (GDFs) regulate homeostasis by amplifying extracellular matrix anabolism and inhibiting pro-inflammatory cytokine production in the intervertebral disc (IVD). The aim of this study was to elucidate the effects of GDF-6 on human IVD nucleus pulposus (NP) cells using a three-dimensional culturing system in vitro and on rat tail IVD tissues using a puncture model in vivo. In vitro, Western blotting showed decreased GDF-6 expression with age and degeneration severity in surgically collected human IVD tissues (n = 12). Then, in moderately degenerated human IVD NP cells treated with GDF-6 (100 ng/mL), immunofluorescence demonstrated an increased expression of matrix components including aggrecan and type II collagen. Quantitative polymerase chain reaction analysis also presented GDF-6-induced downregulation of pro-inflammatory tumor necrosis factor (TNF)-α (p = 0.014) and interleukin (IL)-6 (p = 0.016) gene expression stimulated by IL-1β (10 ng/mL). Furthermore, in the mitogen-activated protein kinase pathway, Western blotting displayed GDF-6-induced suppression of p38 phosphorylation (p = 0.041) under IL-1β stimulation. In vivo, intradiscal co-administration of GDF-6 and atelocollagen was effective in alleviating rat tail IVD annular puncture-induced radiologic height loss (p = 0.005), histomorphological degeneration (p < 0.001), matrix metabolism (aggrecan, p < 0.001; type II collagen, p = 0.001), and pro-inflammatory cytokine production (TNF-α, p < 0.001; IL-6, p < 0.001). Consequently, GDF-6 could be a therapeutic growth factor for degenerative IVD disease.

Self-Assembling Peptide Hydrogels as Functional Tools to Tackle Intervertebral Disc Degeneration

Low back pain (LBP), caused by intervertebral disc (IVD) degeneration, is a major contributor to global disability. In its healthy state, the IVD is a tough and well-hydrated tissue, able to act as a shock absorber along the spine. During degeneration, the IVD is hit by a cell-driven cascade of events, which progressively lead to extracellular matrix (ECM) degradation, chronic inflammation, and pain. Current treatments are divided into palliative care (early stage degeneration) and surgical interventions (late-stage degeneration), which are invasive and poorly efficient in the long term. To overcome these limitations, alternative tissue engineering and regenerative medicine strategies, in which soft biomaterials are used as injectable carriers of cells and/or biomolecules to be delivered to the injury site and restore tissue function, are currently being explored. Self-assembling peptide hydrogels (SAPHs) represent a promising class of de novo synthetic biomaterials able to merge the strengths of both natural and synthetic hydrogels for biomedical applications. Inherent features, such as shear-thinning behaviour, high biocompatibility, ECM biomimicry, and tuneable physiochemical properties make these hydrogels appropriate and functional tools to tackle IVD degeneration. This review will describe the pathogenesis of IVD degeneration, list biomaterials requirements to attempt IVD repair, and focus on current peptide hydrogel materials exploited for this purpose.

Transcription regulators differentiate mesenchymal stem cells into chondroprogenitors, and their in vivo implantation regenerated the intervertebral disc degeneration

BACKGROUND

Intervertebral disc degeneration (IVDD) is the leading cause of lower back pain. Disc degeneration is characterized by reduced cellularity and decreased production of extracellular matrix (ECM). Mesenchymal stem cells (MSCs) have been envisioned as a promising treatment for degenerative illnesses. Cell-based therapy using ECM-producing chondrogenic derivatives of MSCs has the potential to restore the functionality of the intervertebral disc (IVD).

AIM

To investigate the potential of chondrogenic transcription factors to promote differentiation of human umbilical cord MSCs into chondrocytes, and to assess their therapeutic potential in IVD regeneration.

METHODS

MSCs were isolated and characterized morphologically and immunologically by the expression of specific markers. MSCs were then transfected with Sox-9 and Six-1 transcription factors to direct differentiation and were assessed for chondrogenic lineage based on the expression of specific markers. These differentiated MSCs were implanted in the rat model of IVDD. The regenerative potential of transplanted cells was investigated using histochemical and molecular analyses of IVDs.

RESULTS

Isolated cells showed fibroblast-like morphology and expressed CD105, CD90, CD73, CD29, and Vimentin but not CD45 antigens. Overexpression of Sox-9 and Six-1 greatly enhanced the gene expression of transforming growth factor beta-1 gene, BMP, Sox-9, Six-1, and Aggrecan, and protein expression of Sox-9 and Six-1. The implanted cells integrated, survived, and homed in the degenerated intervertebral disc. Histological grading showed that the transfected MSCs regenerated the IVD and restored normal architecture.

CONCLUSION

Genetically modified MSCs accelerate cartilage regeneration, providing a unique opportunity and impetus for stem cell-based therapeutic approach for degenerative disc diseases.

Clinical Development of Regenerative Medicine Targeted for Intervertebral Disc Disease

Low back pain is critical health, social, and economic issue in modern societies. This disease is often associated with intervertebral disc degeneration; however, contemporary treatments are unable to target this underlying pathology to alleviate the pain symptoms. Cell therapy offers a promising novel therapeutic that, in theory, should be able to reduce low back pain through mitigating the degenerative disc environment. With the clinical development of cell therapeutics ongoing, this review aims to summarize reporting on the different clinical trials and assess the different regenerative strategies being undertaken to collectively obtain an impression on the potential safety and effectiveness of cell therapeutics against intervertebral disc-related diseases.

Effects of Growth Factor Combinations TGFβ3, GDF5 and GDF6 on the Matrix Synthesis of Nucleus Pulposus and Nasoseptal Chondrocyte Self-Assembled Microtissues

There has been significant interest in identifying alternative cell sources and growth factor stimulation to improve matrix synthesis for disc repair. Recent work has identified nasoseptal chondrocytes (NC) as a possible alternative cell source with significant matrix-forming abilities. While various growth factors such as members of the TGFβ superfamily have been explored to enhance matrix formation, no consensus exists as to the optimum growth factor needed to induce cells towards a discogenic phenotype. This study assessed both nucleus pulposus (NP) and NC microtissues of different densities (1000, 2500 or 5000 cells/microtissue) stimulated by individual or combinations of the growth factors TGFβ3, GDF5, and GDF6. Lower cell densities result in increased sGAG/DNA and collagen/DNA levels due to higher nutrient availability levels. Our findings suggest that growth factors exert differential effects on matrix synthesis depending on the cell type. NP cells were found to be relatively insensitive to the different growth factor types examined in isolation or in combination. Overall, NCs exhibited a higher propensity to form extracellular matrix compared to NP cells. In addition, stimulating NC-microtissues with GDF5 or TGFβ3 alone induced enhanced matrix formation and may be an appropriate growth factor to stimulate this cell type for disc regeneration.

Degenerative disc disease in young adults: cytokine profile and angiogenic factors

Back pain (BP), associated with the degenerative disc disease (DDD), poses a heavy social and economic burden due to early disability and indications to surgery, emerging in young adults. Pathophysiological basis of premature intervertebral disc (IVD) degeneration is being actively studied. The study was aimed to define the profiles of inflammatory cytokines in DDD, as well as their relationship to the structural spine diseases. The molecular genetic analysis of the mRNA gene abundance in patients with BP and herniated IVD after discectomy and healthy individuals was performed by the quantitative polymerase chain reaction method. High expression of TNFα, IL17 was revealed in the IVD tissues of the affected patients (p < 0.01); the levels of TNFα and IL1β correlated with the DDD severity (r = 0.301 and 0.37; p < 0.05). Elevated expression of IL1β, IL6 was found in peripheral white blood cells (p < 0.01); the levels of IL6 negatively correlated with Modic type 1 and 2 changes (r = –0.31; p < 0.05), and the levels of IL17 positively correlated with the IVD herniation in combination with erosions of the adjacent vertebral body endplates and Modic changes (r = 0.401; p < 0.05). The expression of VEGF-А in the IVD tissues and white blood cells negatively correlated with the DDD grades (r = –0.85; p < 0.001), indicating reduced vascularization in the terminal phase of the disease. The findings on DDD demonstrate the contribution of the local low-immune inflammation, coupled with the intense disc vascularization at the earlier stages, and associated with the reactive inflammation in vertebral bodies. The results are prerequisites for developing the anti-inflammatory and reparative therapy based on the DDD grade and the presence of Modic changes in young adults with BP.

Panax notoginseng saponins attenuate intervertebral disc degeneration by reducing the end plate porosity in lumbar spinal instability mice

Although painkillers could alleviate some of the symptoms, there are no drugs that really cope with the intervertebral disc degeneration (IDD) at present, so it is urgent to find a cure that could prevent or reverse the progression of IDD. During the development of IDD, the cartilaginous end plates (EPs) become hypertrophic and porous by the increase of osteoclast activities, which hinder the penetration of nutrition. The compositional and structural degeneration of the EP may cause both nutritional as well as mechanical impairment to the nucleus pulposus (NP) so that developing drugs that target the degenerating EP may be another option in addition to targeting the NP. In the lumbar spine instability mouse model, we found increased porosity in the cartilaginous EP, accompanied by the decrease in total intervertebral disc volume. Panax notoginseng saponins (PNS), a traditional Chinese patent drug with anti-osteoclastogenesis effect, could alleviate IDD by inhibiting aberrant osteoclast activation in the porous EP. Further in vitro experiment validated that PNS inhibit the receptor activator of nuclear factor kappa-Β ligand-induced osteoclast differentiation, while the transcriptional activation of PAX6 may be involved in the mechanism, which had been defined as an inhibitory transcription factor in osteoclastogenesis. These findings may provide a novel therapeutic strategy for IDD.

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.

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.

circSPG21 protects against intervertebral disc disease by targeting miR-1197/ATP1B3

The abnormal expression of circular RNAs (circRNAs) is associated with numerous human diseases. This study investigated the mechanism by which circRNA acts as competitive endogenous RNA in the regulation of degenerative intervertebral disc disease (IVDD). Decreased expression of circSPG21 was detected in degenerated nucleus pulposus cells (NPCs), the function of circSPG21 in NPCs was explored and verified, and the downstream target of circSPG21 was investigated. The interaction between circSPG21 and miR-1197 and its target gene (ATP1B3) was studied by online database prediction and molecular biological verification. Finally, the circSPG21/miR-1197/ATP1B3 axis was verified in the mouse tail-looping model. The expression of circSPG21 in the nucleus pulposus in IVDD was directly related to an imbalance of anabolic and catabolic factors, which affected cell senescence. circSPG21 was found to play a role in human NPCs by acting as a sponge of miR-1197 and thereby affecting ATP1B3. The regulation of circSPG21 provides a potentially effective therapeutic strategy for IVDD.

Lentivirus-mediated transfer of gene encoding fibroblast growth factor-18 inhibits intervertebral disc degeneration

Fibroblast growth factor 18 (FGF-18) is a well-characterized anabolic growth factor involved in cartilage homeostasis. However, the effect of FGF-18 on intervertebral disc (IVD) degeneration has not been investigated. The present study aimed to investigate the role of FGF-18 in the process of rabbit IVD degeneration. In vitro, primary nucleus pulposus cells (NPs) were cultured and transfected with a lentivirus. Tert-butyl hydroperoxide (TBHP) was used to induce apoptosis in NPs on the second passage, while overexpression of FGF-18 in NPs attenuated TBHP-induced apoptosis. A rabbit annular puncture model was generated to induce IVD degeneration in vivo. The discs were injected with an FGF-18-overexpression lentivirus or a negative control lentivirus. In the sham group, the discs were exposed and not punctured. Disc degeneration was evaluated using H&E staining and a histological grading system. Reverse transcription-quantitative PCR was used to detect the expression of the extracellular matrix-degrading enzymes matrix metalloproteinase-3 (MMP-3) and A disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS-5). Nucleus pulposus apoptosis was detected via western blotting, immunohistochemical methods and TUNEL staining. Histologic examination showed that disc degeneration was attenuated after FGF-18 overexpression treatment. At 8 weeks after surgery, the expression of MMP-3 and ADAMTS-5 in the annular puncture groups was higher compared with in the sham group. FGF-18 treatment inhibited the expression of MMP-3 and ADAMTS-5 at the mRNA level. Western blot assays indicated that the expression level of Bax was significantly reduced in the FGF-18 groups, and that the expression level of Bcl-2 was significantly increased compared with those in the control group. Moreover, immunohistochemical analysis indicated that the FGF-18 group exhibited a lower percentage of cleaved caspase 3-positive NPs. Quantification of the TUNEL staining demonstrated that the FGF-18 group had fewer apoptotic NPs than the control group. These findings indicated that FGF-18 could delay IVD degeneration by inhibiting the apoptosis of NPs and the expression of matrix-degrading enzymes.

TGF-β3-loaded graphene oxide - self-assembling peptide hybrid hydrogels as functional 3D scaffolds for the regeneration of the nucleus pulposus

Intervertebral disc (IVD) degeneration is a process that starts in the central nucleus pulposus (NP) and leads to inflammation, extracellular matrix (ECM) degradation, and progressive loss of disc height. Early treatment of IVD degeneration is critical to the reduction of low back pain and related disability. As such, minimally invasive therapeutic approaches that can halt and reverse NP degeneration at the early stages of the disease are needed. Recently, we developed an injectable graphene oxide (GO) - self-assembling peptide FEFKFEFK (F: phenylalanine; K: lysine; E: glutamic acid) hybrid hydrogels as potential delivery platform for cells and/or drugs in the NP. In this current study, we explored the possibility of using the GO present in these hybrid hydrogels as a vehicle for the sequestration and controlled delivery of transforming growth factor beta-3 (TGF-β3), an anabolic growth factor (GF) known to direct NP cell fate and function. For this purpose, we first investigated the potential of GO to bind and sequestrate TGF-β3. We then cultured bovine NP cells in the new functional scaffolds and investigated their response to the presence of GO and TGF-β3. Our results clearly showed that GO flakes can sequestrate TGF-β3 through strong binding interactions resulting in a slow and prolonged release, with the GF remaining active even when bound to the GO flakes. The adsorption of the GF on the GO flakes to create TGF-β3-loaded GO flakes and their subsequent incorporation in the hydrogels through mixing, [(GO/TGF-β3_Ads)-F8] hydrogel, led to the upregulation of NP-specific genes, accompanied by the production and deposition of an NP-like ECM, rich in aggrecan and collagen II. NP cells actively interacted with TGF-β3-loaded GO flakes and remodeled the scaffolds through endocytosis. This work highlights the potential of using GO as a nanocarrier for the design of functional hybrid peptide-based hydrogels. STATEMENT OF SIGNIFICANCE: Intervertebral disc (IVD) degeneration is a process that starts in the central nucleus pulposus (NP) and leads to inflammation, extracellular matrix (ECM) degradation, and progressive loss of disc height. As such, minimally invasive therapeutic approaches that can halt and reverse NP degeneration at the early stages of the disease are needed. In this current study, we explored the possibility of using peptide - GO hybrid hydrogels as a vehicle for the sequestration and controlled delivery of transforming growth factor beta-3 (TGF-β3), an anabolic growth factor (GF) known to direct NP cell fate and function.

Hepatocyte growth factor regulates HIF-1α-induced nucleus pulposus cell proliferation through MAPK-, PI3K/Akt-, and STAT3-mediated signaling

Intervertebral discs are important for maintaining mobility and offer support to the body trunk. If these discs lose their biomechanical features, lower back pain can occur. We previously reported that hepatocyte growth factor (HGF) promotes cell proliferation and suppresses apoptosis, inflammation, and matrix degradation in nucleus pulposus (NP) cells. In the present study, we investigated the molecular mechanisms of how HGF promotes the proliferation of NP cells in hypoxic conditions. Hypoxic stimulation promoted modest cell proliferation, which was further upregulated by HGF. Expression of hypoxia-inducible factor (HIF-1α) protein, which contributes to the maintenance of homeostasis in NP cells, was also upregulated in hypoxia-treated cell groups; HGF further increased HIF-1α expression in NP cells. Additionally, knockdown of HIF-1α expression significantly reduced the proliferation of NP cells. An MAPK inhibitor inhibited the expression of HIF-1α and pERK, as well as cell proliferation in a dose-dependent manner. Similarly, inhibiting the PI3K/Akt and STAT3 pathways also decreased the expression of HIF-1α and cell proliferation. These results show that under hypoxic conditions, HGF promotes NP cell proliferation via HIF-1α-, MAPK-, PI3K/Akt-, and STAT3-mediated signaling which is involved in this pathway. The control of these signaling pathways may be a target for potential therapeutic strategies for the treatment of disc degeneration in hypoxic conditions.

Effect of Whole Tissue Culture and Basic Fibroblast Growth Factor on Maintenance of Tie2 Molecule Expression in Human Nucleus Pulposus Cells

Previous work showed a link between Tie2⁺ nucleus pulposus progenitor cells (NPPC) and disc degeneration. However, NPPC remain difficult to maintain in culture. Here, we report whole tissue culture (WTC) combined with fibroblast growth factor 2 (FGF2) and chimeric FGF (cFGF) supplementation to support and enhance NPPC and Tie2 expression. We also examined the role of PI3K/Akt and MEK/ERK pathways in FGF2 and cFGF-induced Tie2 expression. Young herniating nucleus pulposus tissue was used. We compared WTC and standard primary cell culture, with or without 10 ng/mL FGF2. PI3K/Akt and MEK/ERK signaling pathways were examined through western blotting. Using WTC and primary cell culture, Tie2 positivity rates were 7.0 ± 2.6% and 1.9 ± 0.3% (p = 0.004), respectively. Addition of FGF2 in WTC increased Tie2 positivity rates to 14.2 ± 5.4% (p = 0.01). FGF2-stimulated expression of Tie2 was reduced 3-fold with the addition of the MEK inhibitor PD98059 (p = 0.01). However, the addition of 1 μM Akt inhibitor, 124015-1MGCN, only reduced small Tie2 expression (p = 0.42). cFGF similarly increased the Tie2 expression, but did not result in significant phosphorylation in both the MEK/ERK and PI3K/Akt pathways. WTC with FGF2 addition significantly increased Tie2 maintenance of human NPPC. Moreover, FGF2 supports Tie2 expression via MEK/ERK and PI3K/Akt signals. These findings offer promising tools and insights for the development of NPPC-based therapeutics.

MicroRNA-140-3p alleviates intervertebral disc degeneration via KLF5/N-cadherin/MDM2/Slug axis

MicroRNAs (miRNAs) are associated with healing or deteriorating degenerated intervertebral disc (IVD) tissues in spinal cord diseases, including intervertebral disc degeneration (IDD). IDD represents a chronic process of extracellular matrix destruction, but the relevant molecular mechanisms implicated in the regenerative effects of miRNAs are unclear. Here, we investigated the regenerative effects of microRNA-140 (miR-140-3p) in an IDD model induced by annulus needle puncture. Bioinformatics analysis was conducted to identify regulatory factors (KLF5/N-cadherin/MDM2/Slug) linked to miR-140-3p effects in IDD. Mesenchymal stem cells (MSCs) were extracted from degenerated IVD nucleus pulposus (NP), and the expression of miR-140-3p/KLF5/N-cadherin/MDM2/Slug was manipulated to explore their effects on cell proliferation, migration, apoptosis and differentiation. The results showed that miR-140-3p was under-expressed in the degenerated IVD NP, whereas its overexpression alleviated IDD. Mechanistic studies suggested that miR-140-3p targeted KLF5 expression, and high KLF5 expression impeded the migration and differentiation of MSCs. In degenerated IVD NP-derived MSCs, MiR-140-3p-mediated KLF5 downregulation simultaneously elevated N-cadherin expression and transcriptionally inhibited MDM2, thus upregulating Slug expression. The experimental data indicated that miR-140-3p enhanced the proliferation, migration and differentiation of degenerated IVD NP-derived MSCs and repressed their apoptosis. The in vivo validation experiment also demonstrated that miR-140-3p inhibited IDD by modulating the KLF5/N-cadherin/MDM2/Slug axis. Collectively, our results uncovered the regenerative role of miR-140-3p in IDD via regulation of the KLF5/N-cadherin/MDM2/Slug axis, which could be a potential therapeutic target for IDD.

Intervertebral Disc Degeneration: The Role and Evidence for Non-Stem-Cell-Based Regenerative Therapies

The use of non-stem-cell-based regenerative medicine therapies for lumbar discogenic pain is an area of growing interest. Although the intervertebral disc is a largely avascular structure, cells located within the nucleus pulposus as well as annulus fibrosis could be targeted for regenerative and restorative treatments. Degenerative disc disease is caused by an imbalance of catabolic and anabolic events within the nucleus pulposus. As catabolic processes overwhelm the environment within the nucleus pulposus, proinflammatory cytokines increase in concentration and lead to further disc degeneration. Non-stem-cell-based therapies, which include growth factor therapy and other proteins, can lead to an increased production of collagen and proteoglycans within the disc.

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

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

A challenging playing field: Identifying the endogenous impediments to annulus fibrosus repair

Intervertebral disc (IVD) herniations, caused by annulus fibrosus (AF) tears that enable disc tissue extrusion beyond the disc space, are very prevalent, especially among adults in the third to fifth decade of life. Symptomatic herniations, in which the extruded tissue compresses surrounding nerves, are characterized by back pain, numbness, and tingling and can cause extreme physical disability. Patients whose symptoms persist after nonoperative intervention may undergo surgical removal of the herniated tissue via microdiscectomy surgery. The AF, however, which has a poor endogenous healing ability, is left unrepaired increasing the risk for re-herniation and pre-disposing the IVD to degenerative disc disease. The lack of understanding of the mechanisms involved in native AF repair limits the design of repair systems that overcome the impediments to successful AF restoration. Moreover, the complexity of the AF structure and the challenging anatomy of the repair environment represents a significant challenge for the design of new repair devices. While progress has been made towards the development of an effective AF repair technique, these methods have yet to demonstrate long-term repair and recovery of IVD biomechanics. In this review, the limitations of endogenous AF healing are discussed and key cellular events and factors involved are highlighted to identify potential therapeutic targets that can be integrated into AF repair methods. Clinical repair strategies and their limitations are described to further guide the design of repair approaches that effectively restore native tissue structure and function.

Site-Directed Differentiation of Human Adipose-Derived Mesenchymal Stem Cells to Nucleus Pulposus Cells Using an Injectable Hydroxyl-Functional Diblock Copolymer Worm Gel

Adipose-derived mesenchymal stem cells (ASCs) have been identified for their promising therapeutic potential to regenerate and repopulate the degenerate intervertebral disk (IVD), which is a major cause of lower back pain. The optimal cell delivery system remains elusive but encapsulation of cells within scaffolds is likely to offer a decisive advantage over the delivery of cells in solution by ensuring successful retention within the tissue. Herein, we evaluate the use of a fully synthetic, thermoresponsive poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer worm gel that mimics the structure of hydrophilic glycosaminoglycans. The objective was to use this gel to direct differentiation of human ASCs toward a nucleus pulposus (NP) phenotype, with or without the addition of discogenic growth factors TGFβ or GDF6. Accordingly, human ASCs were incorporated into a cold, free-flowing aqueous dispersion of the diblock copolymer, gelation induced by warming to 37 °C and cell culture was conducted for 14 days with or without such growth factors to assess the expression of characteristic NP markers compared to those produced when using collagen gels. In principle, the shear-thinning nature of the biocompatible worm gel enables encapsulated human ASCs to be injected into the IVD using a 21G needle. Moreover, we find significantly higher gene expression levels of ACAN, SOX-9, KRT8, and KR18 for ASCs encapsulated within worm gels compared to collagen scaffolds, regardless of the growth factors employed. In summary, such wholly synthetic worm gels offer considerable potential as an injectable cell delivery scaffold for the treatment of degenerate disk disease by promoting the transition of ASCs toward an NP-phenotype.

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

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

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.

Non-viral Gene Delivery Methods for Bone and Joints

Viral carrier transport efficiency of gene delivery is high, depending on the type of vector. However, viral delivery poses significant safety concerns such as inefficient/unpredictable reprogramming outcomes, genomic integration, as well as unwarranted immune responses and toxicity. Thus, non-viral gene delivery methods are more feasible for translation as these allow safer delivery of genes and can modulate gene expression transiently both in vivo, ex vivo, and in vitro. Based on current studies, the efficiency of these technologies appears to be more limited, but they are appealing for clinical translation. This review presents a summary of recent advancements in orthopedics, where primarily bone and joints from the musculoskeletal apparatus were targeted. In connective tissues, which are known to have a poor healing capacity, and have a relatively low cell-density, i.e., articular cartilage, bone, and the intervertebral disk (IVD) several approaches have recently been undertaken. We provide a brief overview of the existing technologies, using nano-spheres/engineered vesicles, lipofection, and in vivo electroporation. Here, delivery for microRNA (miRNA), and silencing RNA (siRNA) and DNA plasmids will be discussed. Recent studies will be summarized that aimed to improve regeneration of these tissues, involving the delivery of bone morphogenic proteins (BMPs), such as BMP2 for improvement of bone healing. For articular cartilage/osteochondral junction, non-viral methods concentrate on targeted delivery to chondrocytes or MSCs for tissue engineering-based approaches. For the IVD, growth factors such as GDF5 or GDF6 or developmental transcription factors such as Brachyury or FOXF1 seem to be of high clinical interest. However, the most efficient method of gene transfer is still elusive, as several preclinical studies have reported many different non-viral methods and clinical translation of these techniques still needs to be validated. Here we discuss the non-viral methods applied for bone and joint and propose methods that can be promising in clinical use.

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

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

Regenerative Response of Degenerate Human Nucleus Pulposus Cells to GDF6 Stimulation

Growth differentiation factor (GDF) family members have been implicated in the development and maintenance of healthy nucleus pulposus (NP) tissue, making them promising therapeutic candidates for treatment of intervertebral disc (IVD) degeneration and associated back pain. GDF6 has been shown to promote discogenic differentiation of mesenchymal stem cells, but its effect on NP cells remains largely unknown. Our aim was to investigate GDF6 signalling in adult human NP cells derived from degenerate tissue and determine the signal transduction pathways critical for GDF6-mediated phenotypic changes and tissue homeostatic mechanisms. This study demonstrates maintained expression of GDF6 receptors in human NP and annulus fibrosus (AF) cells across a range of degeneration grades at gene and protein level. We observed an anabolic response in NP cells treated with recombinant GDF6 (increased expression of matrix and NP-phenotypic markers; increased glycosaminoglycan production; no change in catabolic enzyme expression), and identified the signalling pathways involved in these responses (SMAD1/5/8 and ERK1/2 phosphorylation, validated by blocking studies). These findings suggest that GDF6 promotes a healthy disc tissue phenotype in degenerate NP cells through SMAD-dependent and -independent (ERK1/2) mechanisms, which is important for development of GDF6 therapeutic strategies for treatment of degenerate discs.

NF-κB inhibitor, NEMO-binding domain peptide attenuates intervertebral disc degeneration

BACKGROUND CONTEXT

Nonphysiological mechanical loading and inflammation are both critically involved in intervertebral disc (IVD) degeneration, which is characterized by an increase in cytokines and matrix metalloproteases (MMPs) in the nucleus pulposus (NP). This process is known to be mediated by the NF-κB pathway.

CLINICAL SIGNIFICANCE

Current clinical treatments for IVD degeneration focus on the alleviation of symptoms rather than targeting the underlying mechanism. Injection of an NF-κB inhibitor may attenuate the progression of IVD degeneration.

PURPOSE

To investigate the ability of the NF-κB inhibitor, NEMO binding domain peptide (NBD), to alter IVD degeneration processes by reducing IL-1β- and mechanically-induced cytokine and MMP levels in human nucleus pulposus cells in vitro, and by attenuating IVD degeneration in an in vivo rat model for disc degeneration.

STUDY DESIGN

Experimental in vitro and animal model.

PATIENT SAMPLE

Discarded specimens of lumbar disc from 21 patients, and 12 Sprague Dawley rats.

OUTCOME MEASURES

Gene and protein expression, cell viability, µMRI and histology.

METHODS

IL-1β-prestimulated human nucleus pulposus cells embedded into fibrin constructs were loaded in the Flexcell FX-5000 compression system at 5 kPa and 1 Hz for 48 hours in the presence and absence of NBD. Unloaded hNPC/fibrin constructs served as controls. Cell viability in loaded and unloaded constructs was quantified, and gene and protein expression levels determined. For in vivo testing, a rat needle disc puncture model was employed. Experimental groups included injured discs with and without NBD injection and uninjured controls. Levels of disc degeneration were determined via µMRI, qPCR and histology. Funding sources include $48,874 NASS Young Investigator Research Grant and $119,174 NIH 5K01AR071512-02. There were no applicable financial relationships or conflicts of interest.

RESULTS

Mechanical compression of hNPC/fibrin constructs resulted in upregulation of MMP-3 and IL-8. Supplementation of media with 10 μM NBD during loading increased cell viability, and decreased MMP-3 gene and protein levels. IVD injury in rat resulted in an increase in MMP-3, IL-1β and IL-6 gene expression. Injections of 250 µg of NBD during disc injury resulted in decreased IL-6 gene expression. µMRI analysis demonstrated a reduction of disc hydration in response to disc needle injury, which was attenuated in NBD-treated IVDs. Histological evaluation showed NP and AF lesion in injured discs, which was attenuated by NBD injection.

CONCLUSIONS

The results of this study show NBD peptide's capacity to reduce IL-1β- and loading-induced MMP-3 levels in hNPC/fibrin constructs while increasing the cells' viability, and to attenuate IVD degeneration in rat, involving downregulation of IL-6. Therefore, NBD may be a potential therapeutic agent to treat IVD degeneration.

Advanced Strategies for the Regeneration of Lumbar Disc Annulus Fibrosus

Damage to the annulus fibrosus (AF), the outer region of the intervertebral disc (IVD), results in an undesirable condition that may accelerate IVD degeneration causing low back pain. Despite intense research interest, attempts to regenerate the IVD have failed so far and no effective strategy has translated into a successful clinical outcome. Of particular significance, the failure of strategies to repair the AF has been a major drawback in the regeneration of IVD and nucleus replacement. It is unlikely to secure regenerative mediators (cells, genes, and biomolecules) and artificial nucleus materials after injection with an unsealed AF, as IVD is exposed to significant load and large deformation during daily activities. The AF defects strongly change the mechanical properties of the IVD and activate catabolic routes that are responsible for accelerating IVD degeneration. Therefore, there is a strong need to develop effective therapeutic strategies to prevent or reconstruct AF damage to support operational IVD regenerative strategies and nucleus replacement. By the way of this review, repair and regenerative strategies for AF reconstruction, their current status, challenges ahead, and future outlooks were discussed.