Evaluating Osteogenic Potential of Ligamentum Flavum Cells Cultivated in Photoresponsive Hydrogel that Incorporates Bone Morphogenetic Protein-2 for Spinal Fusion

Dysregulation of metalloproteinases in spinal ligament degeneration

PURPOSE

Degenerative changes in the spinal ligaments, such as hypertrophy or ossification, are important pathophysiological mechanisms of secondary spinal stenosis and neurological compression. Extracellular matrix (ECM) remodeling is one of the major pathological changes in ligament degeneration, and in this remodeling, ECM proteinase-mediated degradation of elastin and collagen plays a vital role. Zinc-dependent endopeptidases, including matrix metalloproteinases (MMPs), a disintegrin and metalloproteinases (ADAMs), and ADAMs with thrombospondin-1 motifs (ADAMTSs) are key factors in ECM remodeling. This review aims to elucidate the underlying mechanisms of these metalloproteinases in the initiation and progression of spinal ligament degeneration.

METHODS

We clarify current literature on the dysregulation of MMPs/ADAMs/ADAMTS and their endogenous inhibitors in degenerative spinal ligament diseases. In addition, some instructive information was excavated from the raw data of the relevant high-throughput analysis.

RESULTS AND CONCLUSIONS

The dysregulation of metalloproteinases and their endogenous inhibitors may affect ligament degeneration by involving several interrelated processes, represented by ECM degradation, fibroblast proliferation, and osteogenic differentiation. Antagonists of the key targets of the processes may in turn ease ligament degeneration.

Administration of N-Acetylcysteine to Regress the Fibrogenic and Proinflammatory Effects of Oxidative Stress in Hypertrophic Ligamentum Flavum Cells

Ligamentum flavum hypertrophy (LFH) is a major cause of lumbar spinal stenosis (LSS). In hypertrophic ligamentum flavum (LF) cells, oxidative stress activates intracellular signaling and induces the expression of inflammatory and fibrotic markers. This study explored whether healthy and hypertrophic LF cells respond differently to oxidative stress, via examining the levels of phosphorylated p38 (p-p38), inducible nitric oxide synthase (iNOS), and α-smooth muscle actin (α-SMA). Furthermore, the efficacy of N-acetylcysteine (NAC), an antioxidant, in reversing the fibrogenic and proinflammatory effects of oxidative stress in hypertrophic LF cells was investigated by assessing the expression levels of p-p38, p-p65, iNOS, TGF-β, α-SMA, vimentin, and collagen I under H2O2 treatment with or without NAC. Under oxidative stress, p-p38 increased significantly in both hypertrophic and healthy LF cells, and iNOS was elevated in only the hypertrophic LF cells. This revealed that oxidative stress negatively affected both hypertrophic and healthy LF cells, with the hypertrophic LF cells exhibiting more active inflammation than did the healthy cells. After H2O2 treatment, p-p38, p-p65, iNOS, TGF-β, vimentin, and collagen I increased significantly, and NAC administration reversed the effects of oxidative stress. These results can form the basis of a novel therapeutic treatment for LFH using antioxidants.

Facilitated and Controlled Strontium Ranelate Delivery Using GCS-HA Nanocarriers Embedded into PEGDA Coupled with Decortication Driven Spinal Regeneration

BACKGROUND AND PURPOSE

Strontium ranelate (SrR) is an oral pharmaceutical agent for osteoporosis. In recent years, numerous unwanted side effects of oral SrR have been revealed. Therefore, its clinical administration and applications are limited. Hereby, this study aims to develop, formulate, and characterize an effective SrR carrier system for spinal bone regeneration.

METHODS

Herein, glycol chitosan with hyaluronic acid (HA)-based nanoformulation was used to encapsulate SrR nanoparticles (SrRNPs) through electrostatic interaction. Afterward, the poly(ethylene glycol) diacrylate (PEGDA)-based hydrogels were used to encapsulate pre-synthesized SrRNPs (SrRNPs-H). The scanning electron microscope (SEM), TEM, rheometer, Fourier-transform infrared spectroscopy (FTIR), and dynamic light scattering (DLS) were used to characterize prepared formulations. The rabbit osteoblast and a rat spinal decortication models were used to evaluate and assess the developed formulation biocompatibility and therapeutic efficacy.

RESULTS

In vitro and in vivo studies for cytotoxicity and bone regeneration were conducted. The cell viability test showed that SrRNPs exerted no cytotoxic effects in osteoblast in vitro. Furthermore, in vivo analysis for new bone regeneration mechanism was carried out on rat decortication models. Radiographical and histological analysis suggested a higher level of bone regeneration in the SrRNPs-H-implanted groups than in the other experimental groups.

CONCLUSION

Local administration of the newly developed formulated SrR could be a promising alternative therapy to enhance bone regeneration in bone-defect sites in future clinical applications.

Mesenchyme homeobox 1 mediated-promotion of osteoblastic differentiation is negatively regulated by mir-3064-5p

Human mesenchymal stem cells (hMSCs) are multipotent cells that can be differentiated into different cell types including osteoblasts. Herein we aimed to assess the regulation of transcription factor mesenchyme homeobox 1 (Meox1) in the osteogenic differentiation of hMSCs and to determine the microRNA which targets on Meox1. Total RNA was extracted from the isolated ligamentum flavum tissue samples and cultured hMSCs, and the expression of Meox1 was assessed by RT-PCR and Western blot assays. Cultured hMSCs were induced towards osteoblastic differentiation, and the osteoblast phenotype was determined by alkaline phosphatase activity and alizarin red staining. The microRNA targeting on the 3'-UTR of Meox1was predicted using bioinformatics tool, and the binding was validated by luciferase and RNA pulldown assays. The osteoblastic differentiation of hMSCs was checked with the knockdown of Meox1 and microRNA inhibitors. Higher expression of Meox1, and lower expression of miR-3064-5p in ossified ligamentum flavum (OLF) tissues were identified. In addition, increased expression along with the osteoblastic differentiation of hMSCs was found. Further research revealed that Meox was a direct target of miR-3064-5p, when the former promoted the differentiation of hMSCs into osteoblasts, the latter significantly suppressed the osteogenesis. The expression of Meox1 increased gradually with the osteoblastic differentiation of hMSCs, during which miR-3064-5p decreased. Meox1 is a direct target of miR-3064-5p, and they both play important roles in the osteogenesis. These findings provide potential target for the development of therapeutic drugs for skeletal system diseases.

The Role of Gene Expression Changes in ceRNA Network Underlying Ossification of Ligamentum Flavum Development

We aimed at exploring the role of gene expression changes regulated by non-coding RNAs in ossification of ligamentum flavum (OLF). Three microarray datasets, including long non-coding RNA (lncRNA)/mRNA expression profile (GSE106253), circular RNA (circRNA) expression profile (GSE106255), and microRNA (miRNA) expression profile (GSE106256), were downloaded from the public Gene Expression Omnibus repository. The differentially expressed (DE) mRNAs, lncRNAs, miRNAs, and circRNAs in OLF tissues were analyzed, compared with normal tissues. Two competing endogenous RNA (ceRNA) networks with lncRNA-miRNA-mRNA and circRNA-miRNA-mRNA interactions were constructed, separately. Random walk with the restart model was applied to calculate the correlations of mRNAs with the published OLF-related genes. The top 50 mRNAs were subjected to function enrichment analysis and active small-molecule prediction. Total 2323 DE mRNAs, 1168 lncRNAs, 336 circRNAs, and 29 miRNAs were identified based on the microarray datasets. The LncRNA-related ceRNA network was constructed with 614 lncRNA-miRNA, 494 miRNA-mRNA, and 2099 lncRNA-mRNA interaction pairs; the circRNA-related ceRNA network was constructed with 153 circRNA-miRNA, 190 miRNA-mRNA, and 210 circRNA-mRNA interaction pairs. There were 17 OLF-related genes retrieved from previous literature, such as NPPS, COL6A1, and COL11A2, among which COL6A1 was the overlapped gene with mRNAs in the ceRNA network. Subsequently, top 50 mRNAs that closely correlated with COL6A1 in the ceRNA network were captured and these genes were closely related with the collagen catabolic process, regulation of cell growth, and neuronal action potential. DRD1 and COL6A1 were predicted to be the targets by small active molecule drugs. The collagen catabolic process may be implicated in OLF development. COL6A1 and DRD1 may be the candidate targets for OLF. However, further validations were needed.

Fabrication of sulphonated poly(ethylene glycol)-diacrylate hydrogel as a bone grafting scaffold

To improve the biological performance of poly(ethylene glycol)-diacrylate (PEGDA) hydrogel as an injectable bone grafting scaffold, sodium methallyl sulphonate (SMAS) was incorporated into PEGDA hydrogel. The physiochemical properties of the resultant polymers were assessed via Fourier transform infrared spectroscopy (FTIR), swelling ratio, zeta potential, surface morphology, and protein adsorption analysis. MC3T3-E1 cells were seeded on the hydrogel to evaluate the effect of the sulphonated modification on their attachment, proliferation, and differentiation. The results of FTIR and zeta potential evaluations revealed that SMAS was successfully incorporated into PEGDA. With increasing concentrations of SMAS, the swelling ratio of the hydrogels increased in deionized water but stayed constant in phosphate buffered saline. The protein adsorption also increased with increasing concentration of SMAS. Moreover, the sulphonated modification of PEGDA hydrogel not only enhanced the attachment and proliferation of osteoblast-like MC3T3-E1 cells but also up-regulated alkaline phosphatase activity as well as gene expression of osteogenic markers and related growth factors, including collagen type I, osteocalcin, runt related transcription factor 2, bone morphogenetic protein 2, and transforming growth factor beta 1. These findings indicate that the sulphonated modification could significantly improve the biological performance of PEGDA hydrogel. Thus, the sulphonated PEGDA is a promising scaffold candidate for bone grafting.

Mechanical stress affects the osteogenic differentiation of human ligamentum flavum cells via the BMP‑Smad1 signaling pathway

The aim of the present study was to investigate the effects of mechanical stress on the osteogenic differentiation of human ligamentum flavum cells via the bone morphogenetic protein (BMP)‑Smad1 signaling pathway. Mechanical stress increased cell proliferation and induced osteogenic differentiation of human cells derived from the ossification of the ligamentum flavum (OLF). In addition, mechanical stress activated osteocalcin (OC), alkaline phosphatase (ALP) and runt‑related transcription factor 2 (RUNX‑2) mRNA expression, and suppressed Ets proto‑oncogene 1 (Ets‑1) and sex determining region Y‑box 2 (SOX‑2) mRNA expression in OLF cells. Src protein expression was suppressed by mechanical stress in human OLF cells. In addition, the protein expression levels of BMP, phosphorylated (p)‑mothers against decapentaplegic homolog‑1 (Smad1) and p‑p38‑mitogen‑activated protein kinases (p38MAPK) were increased by mechanical stress. These results demonstrate that mechanical stress effectively increases cell proliferation, promotes the osteogenic differentiation rate of OLF cells, activates OC, ALP and RUNX‑2, and suppresses Ets‑1 and SOX‑2 potentially via the BMP‑Smad1 and Src‑p38MAPK signaling pathways.