BMP 7 enhances the effect of BMSC s on extracellular matrix remodeling in a rabbit model of intervertebral disc degeneration

Current status and development direction of immunomodulatory therapy for intervertebral disk degeneration

Intervertebral disk (IVD) degeneration (IVDD) is a main factor in lower back pain, and immunomodulation plays a vital role in disease progression. The IVD is an immune privileged organ, and immunosuppressive molecules in tissues reduce immune cell (mainly monocytes/macrophages and mast cells) infiltration, and these cells can release proinflammatory cytokines and chemokines, disrupting the IVD microenvironment and leading to disease progression. Improving the inflammatory microenvironment in the IVD through immunomodulation during IVDD may be a promising therapeutic strategy. This article reviews the normal physiology of the IVD and its degenerative mechanisms, focusing on IVDD-related immunomodulation, including innate immune responses involving Toll-like receptors, NOD-like receptors and the complement system and adaptive immune responses that regulate cellular and humoral immunity, as well as IVDD-associated immunomodulatory therapies, which mainly include mesenchymal stem cell therapies, small molecule therapies, growth factor therapies, scaffolds, and gene therapy, to provide new strategies for the treatment of IVDD.

Cartilage fragments combined with BMSCs-Derived exosomes can promote tendon-bone healing after ACL reconstruction

Anterior cruciate ligament reconstruction (ACLR) often fails due to the inability of tendon-bone integration to regenerate normal tissues and formation of fibrous scar tissues in the tendon-bone interface. Cartilage fragments and exosomes derived from bone mesenchymal stromal cells (BMSCs-Exos) can enhance enthesis healing. Nevertheless, the effects on the tendon-bone healing of ACLR remain unknown. This study found that BMSCs-Exos can promote the proliferation of chondrocytes in cartilage fragments, and activated the expression of chondro-related genes SOX9 and Aggrecan. The optimal effect concentration was 1012 events/uL. Besides, BMSCs-Exos could significantly upregulated the expression of BMP7 and Smad5 in cartilage fragments, and further enhanced the expression of chondrogenic genes. Moreover, this study established a rat model of ACLR and implanted the BMSCs-Exos/cartilage fragment complex into the femoral bone tunnel. Results demonstrated that the mean diameters of the femoral bone tunnels were significantly smaller in the BE-CF group than those in the CF group (p = 0.038) and control group (p = 0.007) at 8 weeks after surgery. Besides, more new bone formation was observed in the femoral tunnels in the BE-CF group, as demonstrated by a larger BV/TV ratio based on the reconstructed CT scans. Histological results also revealed the regeneration of tendon-bone structures, especially fibrocartilage. Thus, these findings provide a promising result that BMSCs-Exos/cartilage fragment complex can prevent the enlargement of bone tunnel and promote tendon-bone healing after ACLR, which may have resulted from the regulation of the BMP7/Smad5 signaling axis.

Can extracellular vesicles be considered as a potential frontier in the treatment of intervertebral disc disease?

As a global public health problem, low back pain (LBP) caused by intervertebral disc degeneration (IDD) seriously affects patients' quality of life. In addition, the prevalence of IDD tends to be younger, which brings a huge burden to individuals and society economically. Current treatments do not delay or reverse the progression of IDD. The emergence of biologic therapies has brought new hope for the treatment of IDD. Among them, extracellular vesicles (EVs), as nanoscale bioactive substances that mediate cellular communication, have now produced many surprising results in the research of the treatment of IDD. This article reviews the mechanisms and roles of EVs in delaying IDD and describes the prospects and challenges of EVs.

A Review: Methodologies to Promote the Differentiation of Mesenchymal Stem Cells for the Regeneration of Intervertebral Disc Cells Following Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration (IDD), a highly prevalent pathological condition worldwide, is widely associated with back pain. Treatments available compensate for the impaired function of the degenerated IVD but typically have incomplete resolutions because of their adverse complications. Therefore, fundamental regenerative treatments need exploration. Mesenchymal stem cell (MSC) therapy has been recognized as a mainstream research objective by the World Health Organization and was consequently studied by various research groups. Implanted MSCs exert anti-inflammatory, anti-apoptotic, and anti-pyroptotic effects and promote extracellular component production, as well as differentiation into IVD cells themselves. Hence, the ultimate goal of MSC therapy is to recover IVD cells and consequently regenerate the extracellular matrix of degenerated IVDs. Notably, in addition to MSC implantation, healthy nucleus pulposus (NP) cells (NPCs) have been implanted to regenerate NP, which is currently undergoing clinical trials. NPC-derived exosomes have been investigated for their ability to differentiate MSCs from NPC-like phenotypes. A stable and economical source of IVD cells may include allogeneic MSCs from the cell bank for differentiation into IVD cells. Therefore, multiple alternative therapeutic options should be considered if a refined protocol for the differentiation of MSCs into IVD cells is established. In this study, we comprehensively reviewed the molecules, scaffolds, and environmental factors that facilitate the differentiation of MSCs into IVD cells for regenerative therapies for IDD.

Ion elemental-optimized layered double hydroxide nanoparticles promote chondrogenic differentiation and intervertebral disc regeneration of mesenchymal stem cells through focal adhesion signaling pathway

Chronic low back pain and dyskinesia caused by intervertebral disc degeneration (IDD) are seriously aggravated and become more prevalent with age. Current clinical treatments do not restore the biological structure and inherent function of the disc. The emergence of tissue engineering and regenerative medicine has provided new insights into the treatment of IDD. We synthesized biocompatible layered double hydroxide (LDH) nanoparticles and optimized their ion elemental compositions to promote chondrogenic differentiation of human umbilical cord mesenchymal stem cells (hUC-MSCs). The chondrogenic differentiation of LDH-treated MSCs was validated using Alcian blue staining, qPCR, and immunofluorescence analyses. LDH-pretreated hUC-MSCs were differentiated prior to transplantation into the degenerative site of a needle puncture IDD rat model. Repair and regeneration evaluated using X-ray, magnetic resonance imaging, and tissue immunostaining 4–12 weeks after transplantation showed recovery of the disc space height and integrated tissue structure. Transcriptome sequencing revealed significant regulatory roles of the extracellular matrix (ECM) and integrin receptors of focal adhesion signaling pathway in enhancing chondrogenic differentiation and thus prompting tissue regeneration. The construction of ion-specific LDH nanomaterials for in situ intervertebral disc regeneration through the focal adhesion signaling pathway provides theoretical basis for clinical transformation in IDD treatment.

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LDH nanoparticles with different elemental compositions are constructed to optimize the chondrogenic differentiation of hUC-MSCs.

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Optimized-LDH pretreated hUC-MSCs transplantation show recovery of disc space height and integrated tissue structure.

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ECM and focal adhesion signaling pathway play significant roles in LDH-promoted cell differentiation and tissue regeneration.

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Ion-specific optimizing LDH provides theoretical basis for clinical transformation on IDD treatment.

BMP7 ameliorates intervertebral disc degeneration in type 1 diabetic rats by inhibiting pyroptosis of nucleus pulposus cells and NLRP3 inflammasome activity

BACKGROUND

Accumulating evidence indicates that intervertebral disc degeneration (IDD) is associated with diabetes mellitus (DM), while the underlying mechanisms still remain elusive. Herein, the current study sought to explore the potential molecular mechanism of IDD in diabetic rats based on transcriptome sequencing data.

METHODS

Streptozotocin (STZ)-induced diabetes mellitus type 1 (T1DM) rats were used to obtain the nucleus pulposus tissues for transcriptome sequencing. Next, differentially expressed genes (DEGs) in transcriptome sequencing data and GSE34000 microarray dataset were obtained and intersected to acquire the candidate genes. Moreover, GO and KEGG enrichment analyses were performed to analyze the cellular functions and molecular signaling pathways primarily regulated by candidate DEGs.

RESULTS

A total of 35 key genes involved in IDD of T1DM rats were mainly enriched in the extracellular matrix (ECM) and cytokine adhesion binding-related pathways. NLRP3 inflammasome activation promoted the pyroptosis of nucleus pulposus cells (NPCs). Besides, BMP7 could affect the IDD of T1DM rats by regulating the inflammatory responses. Additionally, NPCs were isolated from STZ-induced T1DM rats to illustrate the effects of BMP7 on IDD of T1DM rats using the ectopic expression method. Both in vitro and in vivo experiments validated that BMP7 alleviated IDD of T1DM rats by inhibiting NLRP3 inflammasome activation and pyroptosis of NPCs.

CONCLUSION

Collectively, our findings provided novel mechanistic insights for understanding of the role of BMP7 in IDD of T1DM, and further highlighted BMP7 as a potential therapeutic target for preventing IDD in T1DM.

Targeting Autophagy for Developing New Therapeutic Strategy in Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is a prevalent cause of low back pain. IVDD is characterized by abnormal expression of extracellular matrix components such as collagen and aggrecan. In addition, it results in dysfunctional growth, senescence, and death of intervertebral cells. The biological pathways involved in the development and progression of IVDD are not fully understood. Therefore, a better understanding of the molecular mechanisms underlying IVDD could aid in the development of strategies for prevention and treatment. Autophagy is a cellular process that removes damaged proteins and dysfunctional organelles, and its dysfunction is linked to a variety of diseases, including IVDD and osteoarthritis. In this review, we describe recent research findings on the role of autophagy in IVDD pathogenesis and highlight autophagy-targeting molecules which can be exploited to treat IVDD. Many studies exhibit that autophagy protects against and postpones disc degeneration. Further research is needed to determine whether autophagy is required for cell integrity in intervertebral discs and to establish autophagy as a viable therapeutic target for IVDD.

Functionalized self-assembling peptide RADKPS hydrogels promote regenerative repair of degenerated intervertebral discs

Objective: the aim of this study was to investigate whether the functionalized self-assembling peptide hydrogel RADKPS is safe and effective for regenerative repair of degenerative intervertebral discs. Methods: an in vitro degenerative model of human nucleus pulposus cells was constructed by serum starvation culture, and their proliferation, apoptosis and viability were examined after three-dimensional culture with the RADKPS hydrogel. An in vivo degenerative model of the rabbit intervertebral disc was constructed by annulus fibrosus puncture, and the degeneration of the intervertebral disc was evaluated by imaging, histology, immunohistochemistry, and biomechanics after RADKPS hydrogel intervention. Results: through in vitro cell experiments it is shown that human degenerated nucleus pulposus cells after three-dimensional culture with the RADKPS hydrogel still exhibited better proliferation, viability, and low apoptosis rate. Through in vivo animal experiments we found that rabbit degenerated intervertebral discs intervened with the RADKPS hydrogel had higher water content, better histological morphology, more extracellular matrix synthesis, and better biomechanical properties. It is demonstrated that the RADKPS hydrogel may initiate the endogenous repair process through the sustained recruitment and enrichment of nucleus pulposus progenitor cells. Conclusion: it is verified from both in vitro cellular experiments and in vivo animal experiments that the regenerative repair effect of RADKPS, a functionalized self-assembling peptide hydrogel, on degenerated intervertebral discs is safe and effective. It is shown that it would be a new therapeutic approach for the regenerative repair action of intervertebral discs.

Treatment of Intervertebral Disc Degeneration

Intervertebral disc degeneration (IDD) causes a variety of signs and symptoms, such as low back pain (LBP), intervertebral disc herniation, and spinal stenosis, which contribute to high social and economic costs. IDD results from many factors, including genetic factors, aging, mechanical injury, malnutrition, and so on. The pathological changes of IDD are mainly composed of the senescence and apoptosis of nucleus pulposus cells (NPCs), the progressive degeneration of extracellular matrix (ECM), the fibrosis of annulus fibrosus (AF), and the inflammatory response. At present, IDD can be treated by conservative treatment and surgical treatment based on patients' symptoms. However, all of these can only release the pain but cannot reverse IDD and reconstruct the mechanical function of the spine. The latest research is moving towards the field of biotherapy. Mesenchymal stem cells (MSCs) are regard as the potential therapy of IDD because of their ability to self-renew and differentiate into a variety of tissues. Moreover, the non-coding RNAs (ncRNAs) are found to regulate many vital processes in IDD. There have been many successes in the in vitro and animal studies of using biotherapy to treat IDD, but how to transform the experimental data to real therapy which can apply to humans is still a challenge. This article mainly reviews the treatment strategies and research progress of IDD and indicates that there are many problems that need to be solved if the new biotherapy is to be applied to clinical treatment of IDD. This will provide reference and guidance for clinical treatment and research direction of IDD.

Application of stem cells in the repair of intervertebral disc degeneration

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

Effect of Shenfu Injection on Differentiation of Bone Marrow Mesenchymal Stem Cells into Pacemaker-Like Cells and Improvement of Pacing Function of Sinoatrial Node

Sick sinus syndrome (SSS), a complex type of cardiac arrhythmia, is a major health threat to humans. Shenfu injection (SFI), a formula of traditional Chinese medicine (TCM), is effective in improving bradyarrhythmia. However, the underlying mechanism of SFI’s therapeutic effect is subject to few systematic investigations. The purpose of the present research is to examine whether SFI can boost the differentiation effectiveness of bone marrow mesenchymal stem cells (BMSCs) into pacemaker-like cells and whether the transplantation of these cells can improve the pacing function of the sinoatrial node (SAN) in a rabbit model of SSS. BMSCs from New Zealand rabbits were extracted, followed by incubation in vitro. The flow cytometry was utilized to identify the expression of CD29, CD44, CD90, and CD105 surface markers. The isolated BMSCs were treated with SFI, and the whole-cell patch-clamp method was performed to detect hyperpolarization-the activated cyclic nucleotide-gated potassium channel 4 (HCN4) channel current activation curve. The SSS rabbit model was established using the formaldehyde wet dressing method, and BMSCs treated with SFI were transplanted into the SAN of the SSS rabbit model. We detected changes in the body-surface electrocardiogram and recorded dynamic heart rate measurements. Furthermore, transplanted SFI-treated BMSCs were subjected to HE staining, TUNEL staining, qPCR, western blotting, immunofluorescence, immunohistochemistry, and enzyme-linked immunosorbent assay to study their characteristics. Our results indicate that the transplantation of SFI-treated BMSCs into the SAN of SSS rabbits improved the pacing function of the SAN. In vitro data showed that SFI induced the proliferation of BMSCs, promoted their differentiation capacity into pacemaker-like cells, and increased the HCN4 expression in BMSCs. In vivo, the transplantation of SFI treated-BMSCs preserved the function of SAN in SSS rabbits, improved the expression of the HCN4 gene and gap junction proteins (Cx43 and Cx45), and significantly upregulated the expression of cAMP in the SAN, compared to the SSS model group. In summary, the present research demonstrated that SFI might enhance the differentiation capacity of BMSCs into pacemaker-like cells, hence offering a novel approach for the development of biological pacemakers. Additionally, we confirmed the effectiveness and safety of pacemaker-like cells differentiated from BMSCs in improving the pacing function of the SAN.

Hydroxysafflor yellow A attenuates oxidative stress injury-induced apoptosis in the nucleus pulposus cell line and regulates extracellular matrix balance via CA XII

Intervertebral disc degeneration (IVDD) is the main cause of lower back pain. Oxidative stress injury and degradation of the extracellular matrix (ECM) are important factors causing IVDD, while hydroxysafflor yellow A (HSYA) has significant anti-oxidative stress and anti-apoptotic effects. The present study aimed to investigate the protective role of HSYA in IVDD using nucleus pulposus (NP) cells. A Cell Counting Kit-8 assay was used to detect cell viability following HSYA and tert-Butyl hydroperoxide (TBHP) treatment. Cellular reactive oxygen species levels and the level of apoptosis were measured using flow cytometry. The concentration of superoxide dismutase (SOD), malondialdehyde (MDA), catalase (CAT) and glutathione peroxidase GSH-Px were detected using ELISA. DAPI staining was performed for nuclear morphology analysis, while western blot analysis was used to detect apoptotic- and ECM-related protein expression levels. Bioinformatics analysis was used to predict the binding site between HSYA and carbonic anhydrase 12 (CA12; CA XII). NP cells were transfected withsmall interference RNA (siRNA) for CA XII downregulation. Following TBHP treatment, the level of ROS increased significantly, and the concentrations of SOD, CAT and GSH-Px were decreased. In addition, the apoptosis level of the NP cell line significantly increased following TBHP treatment. Furthermore, the expression levels of ECM-related proteins, collagen II and aggrecan were significantly decreased, and the protein expression level of MMP-13 was significantly increased. HSYA (10 µM) could effectively alleviate the effects of TBHP on NP cell apoptosis, oxidative stress damage and the expression level of ECM-related proteins. A binding site was found between HSYA and CA XII. In addition, CA XII-siRNA significantly reduced the increase in the expression level of collagen II and aggrecan proteins and decrease in the expression level of MMP-13 induced by HSYA in the NP cell line. In conclusion, HSYA could attenuate oxidative stress injury and apoptosis induced by TBHP in the NP cell line, and could improve the regulation of ECM balance.

Bone Mesenchymal Stem Cells Promote Extracellular Matrix Remodeling of Degenerated Nucleus Pulposus Cells via the miR-101-3p/EIF4G2 Axis

The etiology of lumbocrural pain is tightly concerned with intervertebral disk degeneration (IDD). Bone mesenchymal stem cell (BMSC)-based therapy bears potentials for IDD treatment. The properties of microRNA (miRNA)-modified BMSCs may be altered. This study investigated the role and mechanism of BMSCs promoting extracellular matrix (ECM) remodeling of degenerated nucleus pulposus cells (NPCs) via the miR-101-3p/EIF4G2 axis. NPCs were collected from patients with IDD and lumbar vertebral fracture (LVF). The expressions of miR-101-3p and ECM-related proteins, Collagen-I (Col-I) and Collagen-II (Col-II), were detected using the reverse transcription-quantitative polymerase chain reaction. The expressions of Col-I and Col-II, major non-collagenous component Aggrecan, and major catabolic factor Matrix metalloproteinase-13 (MMP-13) were detected using Western blotting. BMSCs were cocultured with degenerated NPCs from patients with IDD. Viability and apoptosis of NPCs were measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and flow cytometry. After the degenerated NPCs were transfected with the miR-101-3p inhibitor, the expressions of ECM-related proteins, cell viability, and apoptosis were detected. The targeting relationship between miR-101-3p and EIF4G2 was verified. Functional rescue experiments verified the effects of miR-101-3p and EIF4G2 on ECM remodeling of NPCs. Compared with the NPCs of patients with LVF, the degenerated NPCs of patients with IDD showed downregulated miR-101-3p, Col-II, and Aggrecan expressions and upregulated MMP-13 and Col-I expressions. BMSCs increased the expressions of miR-101-3p, Aggrecan, and Col-II, and decreased the expressions of MMP-13 and Col-I in degenerated NPCs. BMSCs enhanced NPC viability and repressed apoptosis. Downregulation of miR-101-3p suppressed the promoting effect of BMSCs on ECM remodeling. miR-101-3p targeted EIF4G2. Downregulation of EIF4G2 reversed the inhibiting effect of the miR-101-3p inhibitor on ECM remodeling. In conclusion, BMSCs increased the miR-101-3p expression in degenerated NPCs to target EIF4G2, thus promoting the ECM remodeling of NPCs.

Comparison of the differentiation abilities of bone marrow-derived mesenchymal stem cells and adipose-derived mesenchymal stem cells toward nucleus pulposus-like cells in three-dimensional culture

Nucleus pulposus cell (NPC) transplantation can be a potential therapeutic approach for intervertebral disc degeneration (IDD). However, low cell viability has restricted the therapeutic capacity of NPCs, and sources of natural NPCs are limited. Bone marrow-derived mesenchymal stem cells (BMSCs) and adipose-derived mesenchymal stem cells (ADSCs) can be differentiated toward NPC-like cells. However, it is unknown whether there are differences in the abilities of these two cell types to differentiate into NPC-like cells, or which cell type exhibits the best differentiation ability. The present study compared the abilities of BMSCs and ADSCs to differentiate toward NPC-like cells with or without a 3D culture system to lay a foundation for stem cell transplantation therapy for IDD. BMSCs were isolated from the rat whole bone marrow cell using the repeated adherent culture method. ADSCs were isolated from rat adipose tissues in the subcutaneous inguinal region using the enzyme digestion method. Cells were identified using flow cytometry. Cell viability was assessed via Cell Counting Kit-8 assays, and reverse transcription-quantitative PCR and western blotting were carried out to evaluate the expression of NPC markers and chondrocyte-specific genes. Glycosaminoglycans (GAGs) and proteoglycans were examined via Alcian blue and safranin O staining, respectively. ADSCs in 3D culture displayed the highest cell proliferative ability, compared with the 2D culture system and BMSC culture. In addition, ADSCs in 3D culture exhibited increased GAG and proteoglycan synthesis than BMSCs. Compared with BMSCs in 3D culture, ADSCs in 3D culture exhibited higher mRNA and protein expression of NPC marker genes (hypoxia-inducible factor 1-α, glucose transporter 1) and chondrocyte-specific genes (Sox-9, aggrecan and type II collagen). The present findings indicated that ADSCs exhibited a better ability to differentiate into NPC-like cells in 3D culture compared with BMSCs, which may be of value for the regeneration of intervertebral discs using cell transplantation therapy.

Differentially-expressed mRNAs, microRNAs and long noncoding RNAs in intervertebral disc degeneration identified by RNA-sequencing

The underlying molecular mechanisms of intervertebral disc degeneration (IDD) remain unclear. This study aimed to identify the crucial molecules and explore the function of noncoding RNAs and related pathways in IDD. We randomly selected three samples each from an IDD and a spinal cord injury group (control) for RNA-sequencing. We identified 463 differentially-expressed long noncoding RNAs (lncRNAs), 47 differentially-expressed microRNAs (miRNAs), and 1,334 differentially-expressed mRNAs in IDD. Three hundred fifty-eight lncRNAs as cis-regulators could potentially target 865 genes. Protein–protein interaction (PPI) network analysis confirmed that IL-6, VEGFA, IGF1, MMP9, CXCL8, FGF2, IL1B, CCND1, ITGAM, PTPRC, FOS and PTGS2 were hub genes. We built a competing endogenous RNA (ceRNA) network and identified lncRNA XIST–hsa-miR-4775–PLA2G7 and lncRNA XIST–hsa-miR-424-5p–AMOT/TGFBR3 ceRNA axes. Quantitative real-time PCR (qRT-PCR) was implemented in 15 IDD samples and 15 controls to validate differentially-expressed genes in ceRNA axes. From the ceRNA network, gene ontology (GO) enrichment analysis indicated that noncoding RNAs were associated with several biological processes, including extracellular matrix organization, extracellular structure organization, leukocyte migration, and mesenchyme development. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that noncoding RNAs were associated with several pathways including the AGE-RAGE signaling pathway, PI3K-Akt signaling pathway, axon guidance, and osteoclast differentiation. These results indicate that some specific noncoding RNAs and ceRNA axes may be vital during the development of IDD, and may have potential as alternative diagnostic biomarkers as well as novel therapeutic strategies for IDD.

Animal models of regenerative medicine for biological treatment approaches of degenerative disc diseases

Degenerative disc disease (DDD) is a painful, chronic and progressive disease, which is characterized by inflammation, structural and biological deterioration of the intervertebral disc (IVD) tissues. DDD is specified as cell-, age-, and genetic-dependent degenerative process that can be accelerated by environmental factors. It is one of the major causes of chronic back pain and disability affecting millions of people globally. Current treatment options, such as physical rehabilitation, pain management, and surgical intervention, can provide only temporary pain relief. Different animal models have been used to study the process of IVD degeneration and develop therapeutic options that may restore the structure and function of degenerative discs. Several research works have depicted considerable progress in understanding the biological basis of disc degeneration and the therapeutic potentials of cell transplantation, gene therapy, applications of supporting biomaterials and bioactive factors, or a combination thereof. Since animal models play increasingly significant roles in treatment approaches of DDD, we conducted an electronic database search on Medline through June 2020 to identify, compare, and discuss publications regarding biological therapeutic approaches of DDD that based on intradiscal treatment strategies. We provide an up-to-date overview of biological treatment strategies in animal models including mouse, rat, rabbit, porcine, bovine, ovine, caprine, canine, and primate models. Although no animal model could profoundly reproduce the clinical conditions in humans; animal models have played important roles in specifying our knowledge about the pathophysiology of DDD. They are crucial for developing new therapy approaches for clinical applications.

Bone Morphogenetic Proteins for Nucleus Pulposus Regeneration

Matrix production by nucleus pulposus (NP) cells, the cells residing in the center of the intervertebral disc, can be stimulated by growth factors. Bone morphogenetic proteins (BMPs) hold great promise. Although BMP2 and BMP7 have been used most frequently, other BMPs have also shown potential for NP regeneration. Heterodimers may be more potent than single homodimers, but it is not known whether combinations of homodimers would perform equally well. In this study, we compared BMP2, BMP4, BMP6, and BMP7, their combinations and heterodimers, for regeneration by human NP cells. The BMPs investigated induced variable matrix deposition by NP cells. BMP4 was the most potent, both in the final neotissue glysosaminoglycan content and incorporation efficiency. Heterodimers BMP2/6H and BMP2/7H were more potent than their respective homodimer combinations, but not the BMP4/7H heterodimer. The current results indicate that BMP4 might have a high potential for regeneration of the intervertebral disc. Moreover, the added value of BMP heterodimers over their respective homodimer BMP combinations depends on the BMP combination applied.

Improving Cell Therapy Survival and Anabolism in Harsh Musculoskeletal Disease Environments

Cell therapies are an up and coming technology in orthopedic medicine that has the potential to provide regenerative treatments for musculoskeletal disease. Despite numerous cell therapies showing preclinical success for common musculoskeletal indications of disc degeneration and osteoarthritis, there have been mixed results when testing these therapies in humans during clinical trials. A theory behind the mixed success of these cell therapies is that the harsh microenvironments of the disc and knee they are entering inhibit their anabolism and survival. Therefore, there is much ongoing research looking into how to improve the survival and anabolism of cell therapies within these musculoskeletal disease environments. This includes research into improving cell function under specific microenvironmental conditions known to exist in the intervertebral disc (IVD) and knee environment such as hypoxia, low-nutrient conditions, hyperosmolarity, acidity, and inflammation. This research also includes improving differentiation of cells into desired native cell phenotypes to better enhance their survival and anabolism in the knee and IVD. This review highlights the effects of specific musculoskeletal microenvironmental challenges on cell therapies and what research is being done to overcome these challenges. Impact statement While there has been significant clinical interest in using cell therapies for musculoskeletal pathologies in the knee and intervertebral disc, cell therapy clinical trials have had mixed outcomes. The information presented in this review includes the environmental challenges (i.e., acidic pH, inflammation, hyperosmolarity, hypoxia, and low nutrition) that cell therapies experience in these pathological musculoskeletal environments. This review summarizes studies that describe various approaches to improving the therapeutic capability of cell therapies in these harsh environments. The result is an overview of what approaches can be targeted and/or combined to develop a more consistent cell therapy for musculoskeletal pathologies.

Identification of Potential Biomarkers for Intervertebral Disc Degeneration Using the Genome-Wide Expression Analysis

Intervertebral disc degeneration (IDD) is the major cause of low back pain. The current study was aimed to further elucidate the mechanisms underlying it. Microarray data sets GSE70362 containing Thompson degeneration grades I-V were divided into the control and the degenerative group and were analyzed. Differentially expressed genes (DEGs) were screened and clustered, followed by functional enrichment analysis. Then the protein-protein interaction (PPI) network and the microRNA (miRNA) regulatory network were constructed and integratedly analyzed. Finally, modules from the integrated network were mined, and gene ontology and pathway enrichment analysis were performed. DEGs in three clusters had the overall expression trend with the Thompson grades. The upregulated DEGs were associated with protein transport and localization, while the downregulated DEGs were enriched in membrane lipid metabolic process and endocytosis. After the integrated analysis of PPI and miRNA-target interactions, some hub genes such as HSP90B1, RPS4Y1, RPL15, and UTY, as well as hub miRNAs, including miR-124a and miR-506, were screened. Finally, modules in the integrated network were functionally associated with protein targeting, peptide processing, and metabolic process, as well as protein folding. Taken together, our data showed that the protein synthesis, targeting, and localization can be greatly changed to contribute to the progress of IDD. Besides, the related genes such as RPS4Y1 and HSP90B1 would be used as diagnostic and therapeutic targets for IDD.

In vitro evaluation of 3D printed polycaprolactone scaffolds with angle-ply architecture for annulus fibrosus tissue engineering

Tissue engineering of the annulus fibrosus (AF) is currently being investigated as a treatment for intervertebral disc degeneration, a condition frequently associated with low back pain. The objective of this work was to use 3D printing to generate a novel scaffold for AF repair that mimics the structural and biomechanical properties of the native tissue. Multi-layer scaffolds were fabricated by depositing polycaprolactone struts in opposing angular orientations, replicating the angle-ply arrangement of the native AF tissue. Scaffolds were printed with varied strut diameter and spacing. The constructs were characterized morphologically and by static and dynamic mechanical analyses. Scaffold surfaces were etched with unidirectional grooves and the influence on bovine AF cell metabolic activity, alignment, morphology and protein expression was studied in vitro. Overall, the axial compressive and circumferential tensile properties of the scaffolds were found to be in a similar range to the native AF tissue. Confocal microscopy images indicated that cells were able to attach and spread on the smooth polycaprolactone scaffolds, but the surface texture induced cellular alignment and proliferation. Furthermore, immunofluorescence analysis demonstrated the aligned deposition of collagen type I, aggrecan and the AF-specific protein marker tenomodulin on the etched scaffolds. Overall, results demonstrated the potential for using the scaffolds as a template for AF regeneration.

Use of Allogeneic Hypoxic Mesenchymal Stem Cells For Treating Disc Degeneration in Rabbits

Intervertebral discs (IVDs) are important biomechanical components of the spine. Once degenerated, mesenchymal stem cell (MSC)-based therapies may aid in the repair of these discs. Although hypoxic preconditioning enhances the chondrogenic potential of MSCs, it is unknown whether bone marrow MSCs expanded under hypoxic conditions (1% O₂ , here referred to as hypoxic MSCs) are better than bone marrow MSCs expanded under normoxic conditions (air, here referred to as normoxic MSCs) with regards to disc regeneration capacity. The purpose of this study was to compare the therapeutic effects of hypoxic and normoxic MSCs in a rabbit needle puncture degenerated disc model after intra-disc injection. Six weeks after needle puncture, MSCs were injected into the IVD. A vehicle-treated group and an un-punctured sham-control group were included as controls. The tissues were analyzed by histological and immunohistochemical methods 6 and 12 weeks post-injection. At 6 and 12 weeks, less disc space narrowing was evident in the hypoxic MSC-treated group compared to the normoxic MSC-treated group. Significantly better histological scores were observed in the hypoxic MSC group. Discs treated with hypoxic MSCs also demonstrated significantly better extracellular matrix deposition in type II and XI collagen. Increased CD105 and BMP-7 expression were also observed upon injection of hypoxic MSCs. In conclusion, hypoxic MSC injection was more effective than normoxic MSC injection for reducing IVD degeneration progression in vivo. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1440-1450, 2019.

Intradiscal Injection of Induced Pluripotent Stem Cell-Derived Nucleus Pulposus-Like Cell-Seeded Polymeric Microspheres Promotes Rat Disc Regeneration

Background

Cell replacement therapy is an attractive alternative for treating degenerated intervertebral discs (IVDs), which are related to the reduction of nucleus pulposus-like cells (NP-lCs) and the loss of the extracellular matrix. Induced pluripotent stem cells (iPSCs) which resemble embryonic stem cells are considered to be a potential resource for restoring NP-lCs and disc homeostasis. Here, we proposed an efficient two-step differentiation protocol of human iPSCs into NP-lCs and continuously tested their in vivo ability to regenerate IVDs.

Methods

A polymeric gelatin microsphere (GM) was generated for sustained release of growth and differentiation factor-5 (GDF-5) and as a cell delivery vehicle of NP-lCs. By injecting NP-lC-seeded GDF-5-loaded GMs into the rat coccygeal intervertebral discs, the disc height and water content were examined with the molybdenum target radiographic imaging test and magnetic resonance imaging examination. Histology and immunohistochemistry results were shown with H&E, S-O-Fast Green, and immunohistochemistry staining.

Results

We demonstrated that the injection of NP-lC-seeded GDF-5-loaded GMs could reverse IDD in a rat model. The imaging examination indicated that disc height recovered and water content increased. Histology and immunohistochemistry results indicated that the NP cells as well as their extracellular matrix were partially restored.

Conclusions

The results suggest that NP-lC-seeded GDF-5-loaded GMs could partially regenerate degenerated intervertebral discs after transplantation into rat coccygeal intervertebral discs. Our study will help develop a promising method of stem cell-based therapy for IDD.

Role of heparan sulfate 6-0 endosulfatases in intervertebral disc homeostasis

The expression of heparan sulfate endosulfatases (Sulfs) was investigated in the intervertebral disc (IVD) to clarify their role in IVD homeostasis. Sulf-1 and -2 expression were elucidated in normal and degenerated human IVD. Age-related effects on Sulf expression, type II collagen levels, and structural changes were analyzed in IVDs of wild-type (WT) and Sulf-1 knockout (Sulf-1⁻/⁻) mice. The effect of recombinant Sulf-1 (100 ng/ml) and Sulf-1 knockdown on heparan sulfate proteoglycan and collagen expression in ATDC5 cells were examined. Finally, the effect of Sulf-1 on transforming growth factor (TGF) β1-induced signaling was evaluated. Results show that Sulf-1 and -2 levels were higher in degenerated human IVDs. In WT mice, Sulf-1 and -2 expression generally declined as the animals aged. In particular, Sulf-1 in the nucleus pulposus was higher compared with Sulf-2 at the age of 1 and 6 months and significantly declined with aging. Sulf-1⁻/⁻ mice showed more severe IVD pathology than WT mice, with lower type II collagen levels in nucleus pulposus, and degeneration with type I collagen in annulus fibrosus. In vitro, Sulf-1 induced type II collagen expression and significantly increased TGF-β1-induced Smad2/3 phosphorylation in ATDC5 cells. In conclusion, Sulf-1 might play a critical role from development to maintenance of IVD homeostasis by regulating collagen expression.

Potential therapeutic role of Co-Q10 in alleviating intervertebral disc degeneration and suppressing IL-1β-mediated inflammatory reaction in NP cells

Coenzyme Q10 (Co-Q10) is extraordinarily popular and has been used in abundant interventions as an antioxidant reagent that participates in numerous oxidation reactions. According to substantial evidence previously reported, interleukin-1β (IL-1β) is deemed to be one of the chief orchestrator molecules in the degeneration of intervertebral disc (IVD). However, it is unknown whether Co-Q10 is able to protect against IVD degeneration. In the current study, mouse-derived IVDs as well as primary human nucleus pulposus (NP) cells were isolated and cultured. NP cells were stimulated with IL-1β, with or without selective addition of Co-Q10 to investigate the therapeutic effect of Co-Q10 on IVD degeneration. Levels of IL-1β-induced inflammatory biomarkers including TNF-α, COX-2, IL-6 and iNOS were reduced by Co-Q10, which was possibly associated with inhibition of NF-κB signaling activation. Furthermore, Co-Q10 maintained the production of anabolic biomarkers in NP cells such as collagen 2, aggrecan and Sox-9 and altered the enhanced catabolism induced by IL-1β. Moreover, the therapeutic role of Co-Q10 in sustaining IVD tissue-enhanced anabolism is potentially dependent on activation of the Akt signaling pathway. In summary, Co-Q10 may potentially represent an available molecular target that may shed light on approaches to the prevention and treatment of IVD degeneration in the future.

Current insights on use of growth factors as therapy for Intervertebral Disc Degeneration

Chronic low back pain is a critical health problem and a leading cause of disability in aging populations. A major cause of low back pain is considered to be the degeneration of the intervertebral disc (IVD). Recent advances in therapeutics, particularly cell and tissue engineering, offer potential methods for inhibiting or reversing IVD degeneration, which have previously been impossible. The use of growth factors is under serious consideration as a potential therapy to enhance IVD tissue regeneration. We reviewed the role of chosen prototypical growth factors and growth factor combinations that have the capacity to improve IVD restoration. A number of growth factors have demonstrated potential to modulate the anabolic and anticatabolic effects in both in vitro and animal studies of IVD tissue engineering. Members of the transforming growth factor-β superfamily, IGF-1, GDF-5, BMP-2, BMP-7, and platelet-derived growth factor have all been investigated as possible therapeutic options for IVD regeneration. The role of growth factors in IVD tissue engineering appears promising; however, further extensive research is needed at both basic science and clinical levels before its application is appropriate for clinical use.

Stem cell-based gene delivery mediated by cationic niosomes for bone regeneration

Bone morphogenetic protein-7(BMP-7) plays a pivotal role in the transformation of mesenchymal stem cells (MSCs) into bone. However, its impact is hampered due to its short half-life. Therefore, gene therapy may be an interesting approach to deliver BMP-7 gene to D1-MSCs. In this manuscript we prepared and characterized niosomes based on cationic lipid 2,3-di(tetradecyloxy)propan-1-amine, combined with polysorbate 80 for gene delivery purposes. Niosomes were characterized and combined initially with pCMS-EGFP reporter plasmid, and later with pUNO1-hBMP-7 plasmid to evaluate osteogenesis differentiation. Additionally, specific blockers of most relevant endocytic pathways were used to evaluate the intracellular disposition of complexes. MSCs transfected with niosomes showed increased growth rate, enhanced alkaline phosphatase activity (ALP) and extracellular matrix deposition which suggested the formation of osteoblast-like cells. We concluded that hBMP-7-transfected MSCs could be considered not only as an effective delivery tool of hBMP-7, but also as proliferating and bone forming cells for bone regeneration.

Ghrelin protects against nucleus pulposus degeneration through inhibition of NF-κB signaling pathway and activation of Akt signaling pathway

The objective of the present study was to examine the potential role of ghrelin in degeneration of nucleus pulposus (NP). Lower expression levels of ghrelin were found in human NP cells stimulated with interleukin-1β (IL-1β). Moreover, exogenous ghrelin suppressed IL-1β induced degeneration and inflammation associated biomarkers in human NP cells, including matrix metalloproteinase-13, a disintegrin and metalloproteinase with thrombospondin motifs-5, tumor necrosis factor-α and iNOS, which was possibly mediated by antagonization of NF-κB signaling. Moreover, ghrelin enhanced production of critical extracellular matrix of NP cells, including collagen 2, aggrecan, and Sox-9 in NP cells. Ghrelin also promoted NP tissue regeneration in a rabbit IVD degeneration model, which seems to be associated with growth hormone secretagogue receptor. Additionally, the protective role of ghrelin in anabolism potentially relies on activation of Akt signaling pathway. Taken together, ghrelin may represent a molecular target for prevention and treatment of intervertebral disc degeneration.

Kaempferol slows intervertebral disc degeneration by modifying LPS-induced osteogenesis/adipogenesis imbalance and inflammation response in BMSCs

Intervertebral disc (IVD) degeneration is a common disease that represents a significant cause of socio-economic problems. Bone marrow-derived mesenchymal stem cells (BMSCs) are a potential autologous stem cell source for the nucleus pulposus regeneration. Kaempferol has been reported to exert protective effects against both osteoporosis and obesity. This study explored the effect of kaempferol on BMSCs differentiation and inflammation. The results demonstrated that kaempferol did not show any cytotoxicity at concentrations of 20, 60 and 100μM. Kaempferol enhanced cell viability by counteracting the lipopolysaccharide (LPS)-induced cell apoptosis and increasing cell proliferation. Western blot analysis of mitosis-associated nuclear antigen (Ki67) and proliferation cell nuclear antigen (PCNA) further confirmed the increased effect of kaempferol on LPS-induced decreased viability of BMSCs. Besides, kaempferol elevated LPS-induced reduced level of chondrogenic markers (SOX-9, Collagen II and Aggrecan), decreased the level of matrix-degrading enzymes, i.e., matrix metalloprotease (MMP)-3 and MMP-13, suggesting the osteogenesis of BMSC under kaempferol treatment. On the other hand, kaempferol enhanced LPS-induced decreased expression of lipid catabolism-related genes, i.e., carnitine palmitoyl transferase-1 (CPT-1). Kaempferol also suppressed the expression of lipid anabolism-related genes, i.e., peroxisome proliferators-activated receptor-γ (PPAR-γ). The Oil red O staining further convinced the inhibition effect of kaempferol on BMSCs adipogenesis. In addition, kaempferol alleviated inflammatory by reducing the level of pro-inflammatory cytokines (i.e., interleukin (IL)-6) and increasing anti-inflammatory cytokine (IL-10) via inhibiting the nucleus translocation of nuclear transcription factor (NF)-κB p65. Taken together, our research indicated that kaempferol may serve as a novel target for treatment of IVD degeneration.