Advances and Prospects in Biomaterials for Intervertebral Disk Regeneration

Low-back and neck-shoulder pains caused by intervertebral disk degeneration are highly prevalent among middle-aged and elderly people globally. The main therapy method for intervertebral disk degeneration is surgical intervention, including interbody fusion, disk replacement, and diskectomy. However, the stress changes caused by traditional fusion surgery are prone to degeneration of adjacent segments, while non-fusion surgery has problems, such as ossification of artificial intervertebral disks. To overcome these drawbacks, biomaterials that could endogenously regenerate the intervertebral disk and restore the biomechanical function of the intervertebral disk is imperative. Intervertebral disk is a fibrocartilaginous tissue, primarily comprising nucleus pulposus and annulus fibrosus. Nucleus pulposus (NP) contains high water and proteoglycan, and its main function is absorbing compressive forces and dispersing loads from physical activities to other body parts. Annulus fibrosus (AF) is a multilamellar structure that encloses the NP, comprises water and collagen, and supports compressive and shear stress during complex motion. Therefore, different biomaterials and tissue engineering strategies are required for the functional recovery of NP and AF based on their structures and function. Recently, great progress has been achieved on biomaterials for NP and AF made of functional polymers, such as chitosan, collagen, polylactic acid, and polycaprolactone. However, scaffolds regenerating intervertebral disk remain unexplored. Hence, several tissue engineering strategies based on cell transplantation and growth factors have been extensively researched. In this review, we summarized the functional polymers and tissue engineering strategies of NP and AF to endogenously regenerate degenerative intervertebral disk. The perspective and challenges of tissue engineering strategies using functional polymers, cell transplantation, and growth factor for generating degenerative intervertebral disks were also discussed.

Intervertebral Disk Degeneration: The Microenvironment and Tissue Engineering Strategies

Intervertebral disk degeneration (IVDD) is a leading cause of disability. The degeneration is inevitable, and the mechanisms are complex. Current therapeutic strategies mainly focus on the relief of symptoms, not the intrinsic regeneration of the intervertebral disk (IVD). Tissue engineering is a promising strategy for IVDD due to its ability to restore a healthy microenvironment and promote IVD regeneration. This review briefly summarizes the IVD anatomy and composition and then sets out elements of the microenvironment and the interactions. We rationalized different scaffolds based on tissue engineering strategies used recently. To fulfill the complete restoration of a healthy IVD microenvironment, we propose that various tissue engineering strategies should be combined and customized to create personalized therapeutic strategies for each individual.

MiR-330-5p inhibits intervertebral disk degeneration via targeting CILP

Background Intervertebral disk degeneration (IDD) is caused by nucleus pulposus (NP) degeneration and extracellular matrix (ECM) remodeling and cartilage intermediate layer protein (CILP) expression has been confirmed to be increased in IDD. This study is mainly conducted to clarify the mechanism of CILP in the NP cell degeneration and ECM remodeling in IDD. Methods CILP expression in the degenerated NP tissues and cells is quantified by quantitative real-time PCR and western blot. CILP function is assessed by cell cycle assay, 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and flow cytometry, β-galactosidase staining, and the detection of ECM-related molecules aggrecan, collagen type I, collagen type II, MMP-3, and MMP-9 expression is accomplished by qRT-PCR. The potential mechanism is authenticated by dual-luciferase reporter gene assay. Results CILP was increased in the degenerated NP tissues and cells, and the knockdown of CILP promoted the NP cell cycle, increased cell activity, and repressed cell apoptosis and repressed cell senescence and ECM production. Moreover, miR-330-5p targeted the CILP 3′-untranslated region, and miR-330-5p negatively regulated CILP expression. Moreover, the overexpression of miR-330-5p repressed NP cell degeneration and ECM remodeling to relieve IDD by downregulating CILP. Conclusion MiR-330-5p represses NP cell degeneration and ECM remodeling to ameliorate IDD by downregulating CILP.

Melatonin Attenuates Intervertebral Disk Degeneration via Maintaining Cartilaginous Endplate Integrity in Rats

ObjectiveThe aim of this study is to verify whether melatonin (Mel) could mitigate intervertebral disk degeneration (IVDD) in rats and to investigate the potential mechanism of it.MethodA rat acupuncture model of IVDD was established with intraperitoneal injection of Mel. The effect of Mel on IVDD was analyzed via radiologic and histological evaluations. The specific Mel receptors were investigated in both the nucleus pulposus (NP) and cartilaginous endplates (EPs). In vitro, EP cartilaginous cells (EPCs) were treated by different concentrations of Mel under lipopolysaccharide (LPS) and Luzindole conditions. In addition, LPS-induced inflammatory response and matrix degradation following nuclear factor kappa-B (NF-κB) pathway activation were investigated to confirm the potential mechanism of Mel on EPCs.ResultsThe percent disk height index (%DHI) and MRI signal decreased after initial puncture in the degeneration group compared with the control group, while Mel treatment protected disk height from decline and prevented the loss of water during the degeneration process. In the meantime, the histological staining of the Mel groups showed more integrity and well-ordered construction of the NP and EPs in both low and high concentration than that of the degeneration group. In addition, more deep-brown staining of type II collagen (Coll-II) was shown in the Mel groups compared with the degeneration group. Furthermore, in rat samples, immunohistochemical staining showed more positive cells of Mel receptors 1a and 1b in the EPs, instead of in the NP. Moreover, evident osteochondral lacuna formation was observed in rat EPs in the degeneration group; after Mel treatment, the osteochondral destruction alleviated accompanying fewer receptor activator for nuclear factor-κB ligand (RANKL) and tartrate-resistant acid phosphatase (TRAP)-stained positive cells expressed in the EPs. In vitro, Mel could promote the proliferation of EPCs, which protected EPCs from degeneration under LPS treatment. What is more, Mel downregulated the inflammatory response and matrix degradation of EPCs activated by NF-κB pathway through binding to its specific receptors.ConclusionThese results indicate that Mel protects the integrity of the EPs and attenuates IVDD by binding to the Mel receptors in the EPs. It may alleviate the inflammatory response and matrix degradation of EPCs activated by NF-κB pathway.

Circ_0040039 May Aggravate Intervertebral Disk Degeneration by Regulating the MiR-874-3p-ESR1 Pathway

The functional alteration of nucleus pulposus cells (NPCs) exerts a crucial role in the occurrence and progression of intervertebral disk degeneration (IDD). Circular RNAs and microRNAs (miRs) are critical regulators of NPC metabolic processes such as growth and apoptosis. In this study, bioinformatics tools, encompassing Gene Ontology pathway and Venn diagrams analysis, and protein–protein interaction (PPI) network construction were used to identify functional molecules related to IDD. PPI network unveiled that ESR1 was one of the most critical genes in IDD. Then, a key IDD-related circ_0040039-miR-874-3p-ESR1 interaction network was predicted and constructed. Circ_0040039 promoted miR-874-3p and repressed ESR1 expression, and miR-874-3p repressed ESR1 expression in NPCs, suggesting ESR1 might be a direct target of miR-874-3p. Functionally, circ_0040039 could enhance NPC apoptosis and inhibit NPC growth, revealing that circ_0040039 might aggravate IDD by stabilizing miR-874-3p and further upregulating the miR-874-3p-ESR1 pathway. This signaling pathway might provide a novel therapeutic strategy and targets for the diagnosis and therapy of IDD-related diseases.

Raloxifene retards the progression of adjacent segmental intervertebral disc degeneration by inhibiting apoptosis of nucleus pulposus in ovariectomized rats

Background Adjacent segmental intervertebral disk degeneration (ASDD) is a major complication secondary to lumbar fusion. Although ASSD pathogenesis remains unclear, the primary cause of intervertebral disk degeneration (IVDD) development is apoptosis of nucleus pulposus (NP). Raloxifene (RAL) could delay ASDD by inhibiting NP apoptosis. Methods An ASDD rat model was established by ovariectomy (OVX) and posterolateral spinal fusion (PLF) on levels 4–5 of the lumbar vertebrae. Rats in the treatment groups were administered 1 mg/kg/d RAL by gavage for 12 weeks, following which, all animals were euthanized. Lumbar fusion, apoptosis, ASDD, and vertebrae micro-architecture were evaluated. Results RAL maintained intervertebral disk height (DHI), delayed vertebral osteoporosis, reduced histological score, and inhibited apoptosis. The OVX+PLF+RAL group revealed upregulated expression of aggrecan and B-cell lymphoma-2 (bcl2), as well as significantly downregulated expression of a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS-4), metalloproteinase-13 (MMP-13), caspase-3, BCL2-associated X (bax), and transferase dUTP nick end labeling (TUNEL) staining. Micro-computed tomography (Micro-CT) analysis revealed higher bone volume fraction (BV/TV), bone mineral density (BMD), and trabecular number (Tb.N), and lower trabecular separation (Tb.Sp) in OVX+PLF+RAL group than in the OVX+PLF group. Conclusions RAL can postpone ASDD development in OVX rats through inhibiting extracellular matrix metabolic imbalance, NP cell apoptosis, and vertebral osteoporosis. These findings showed RAL as a potential therapeutic target for ASDD.

A Novel Rat Tail Needle Minimally Invasive Puncture Model Using Three-Dimensional Printing for Disk Degeneration and Progressive Osteogenesis Research

Many studies focused on the annulus fibrosus (AF) injury in rodent tail model for the intervertebral disk degeneration (IDD) research. However, previous studies caused tremendous injury of intervertebral disk (IVD) by penetrating whole disk. This study aimed to build a progressive IDD rodent tail model by a novel device for precise and minimally invasive puncture in AF. A precise puncture device was customized by 3D Printing Technique. 40 rodent tail IVDs were randomly grouped as follows: group A, non-puncture; group B, annulus needle puncture (ANP) for 4 week; group C, ANP for 8 week; and group D, ANP for 12 week. Pre- and post-puncture IVD height on radiographs and IVD signal intensity on T2 magnetic resonance imaging (MRI) were measured. Average bone density (ABD) on the end of coccygeal vertebrae between punctured disk was measured on the radiographs. Hematoxylin and eosin, TUNEL staining methods, immunofluorescence for cleaved-caspas3 and immunohistochemistry for aggrecan and collagen II were performed. Progressively and significantly increasing IVD height loss and degenerative grade were observed following the time points. The ABD was respectively, 81.20 ± 4.63 in group A, 83.93±3.18 in group B, 92.65 ± 4.32 in group C, 98.87 ± 6.69 in group D. In both group C and group D, there were significant differences with group A. In histology, increasing number of AF cells was noted in group B. In both group C and D, the fissures in AF were obviously observed, and a marked reduction of AF cells were also observed. In all ANP groups, there were significant decrease in number of NP cells, as well as aggrecan and collagen II contents. TUNEL assay showed cellular apoptosis were stimulated in all puncture group, especially in group D. A progressive IDD rat model could be standardly established by the micro-injury IVD puncture using a novel 3D printing device. This animal model provided a potential application for research of progressive hyperosteogeny following IDD development.

Effect of Congenital C4–5 Synostosis on Adjacent Mobile Segments: Radiographic Assessment

Study Design: Prospective case series.Purpose: To assess the corporal morphology of the fused body and adjacent segment conditions.Overview of Literature: It is known that two fused vertebral bodies take the similar shape of the single body with inwaisting, with or without caudal flaring of the fused body, and that the fused body can cause the fusion disease at the adjacent segment that can be a risk factor for potential neurological compromise.Methods: Radiograms of the 11 study subjects (six men and five women), aged 22–90 years who visited the outpatients’ clinic for various neck complaints without trauma history were examined. C4–5 synostosis was an incidental finding in all the subjects.Results: All the fused bodies were inwaisted and had anterior caudal breaking but no interior corporal flaring. Adjacent segment disease was not found in eight patients aged <40 years. Disk degeneration was found at C3–4 and C5–6 in three patients each and at C6–7 in two patients. Disk degeneration was limited to the adjacent segments.Conclusions: Degenerative disk changes are associated with the natural aging process, and the corporal morphology of the fused vertebral becomes inwaisted similar to that in the single vertebrae.