Bedside to bench and back to bedside: Translational implications of targeted intervertebral disc therapeutics

Role of Nrf2 and HO-1 in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common age-related disease with clinical manifestations of lumbar and leg pain and limited mobility. The pathogenesis of IDD is mainly mediated by the death of intervertebral disc (IVD) cells and the imbalance of extracellular matrix (ECM) synthesis and degradation. Oxidative stress and inflammatory reactions are the important factors causing this pathological change. Therefore, the regulation of reactive oxygen species and production of inflammatory factors may be an effective strategy to delay the progression of IDD. In recent years, nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream regulated protein heme oxygenase-1 (HO-1) have received special attention due to their antioxidant, anti-inflammatory and anti-apoptotic protective effects. Recent studies have elucidated the important role of these two proteins in the treatment of IDD disease. However, Nrf2 and HO-1 have not been systematically reported in IDD-related diseases. Therefore, this review describes the biological characteristics of Nrf2 and HO-1, the relationship between Nrf2- and HO-1-regulated oxidative stress and the inflammatory response and IDD, and the progress in research on some extracts targeting Nrf2 and HO-1 to improve IDD. Understanding the role and mechanism of Nrf2 and HO-1 in IDD may provide novel ideas for the clinical treatment and development of Nrf2- and HO-1-targeted drugs.

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.

Spondylodiscitis due to Cutibacterium acnes following lumbosacral intradiscal biologic therapy: a case report

A 40-year-old woman with a history of chronic low back pain underwent a fluoroscopically guided intradiscal platelet-rich plasma injection (PRP) at the L5-S1 level. She subsequently developed progressive low back pain, night sweats and decreased ability to ambulate. Laboratory work-up revealed elevated acute phase reactants and imaging revealed L5-S1 intervertebral disc and vertebral end-plate abnormalities highly suggestive of spondylodiscitis. Computed tomography-guided aspiration and biopsy cultures grew Cutibacterium acnes and the patient was subsequently treated with intravenous antibiotics without surgical management. To the best of our knowledge, this is the first published case of lumbar spondylodiscitis following an intradiscal PRP injection, and brings to the forefront several clinically relevant issues including the antimicrobial effects of PRP, the role of C. acnes in spine infections and the ideal treatment protocol for intradiscal biologics in order to minimize morbidity and optimize functional outcomes.

Substrate stiffness- and topography-dependent differentiation of annulus fibrosus-derived stem cells is regulated by Yes-associated protein

Annulus fibrosus (AF) tissue engineering has attracted increasing attention as a promising therapy for degenerative disc disease (DDD). However, regeneration of AF still faces many challenges due to the tremendous complexity of this tissue and lack of in-depth understanding of the structure-function relationship at cellular level within AF is highly required. In light of the fact that AF is composed of various types of cells and has gradient mechanical, topographical and biochemical features along the radial direction. In this study, we aimed to achieve directed differentiation of AF-derived stem cells (AFSCs) by mimicking the mechanical and topographical features of native AF tissue. AFSCs were cultured on four types of electrospun poly(ether carbonate urethane)urea (PECUU) scaffolds with various stiffness and fiber size (soft, small size; stiff, small size; soft, large size and stiff, large size). The results show that with constant fiber size, the expression level of the outer AF (oAF) phenotypic marker genes in AFSCs increased with the scaffold stiffness, while that of inner AF (iAF) phenotypic marker genes showed an opposite trend. When scaffold stiffness was fixed, the expression of oAF phenotypic marker genes in AFSCs increased with fiber size. While the expression of iAF phenotypic marker genes decreased. Such substrate stiffness- and topography-dependent changes of AFSCs was in accordance with the genetic and biochemical distribution of AF tissue from the inner to outer regions. Further, we found that the Yes-associated protein (YAP) was translocated to the nucleus in AFSCs cultured with increasing stiffness and fiber size of scaffolds, yet it remained mostly phosphorylated and cytosolic in cells on soft scaffolds with small fiber size. Inhibition of YAP down-regulated the expression of tendon/ligament-related genes, whereas expression of the cartilage-related genes was upregulated. The results illustrate that matrix stiffness is a potent regulator of AFSC differentiation. Moreover, we reveal that fiber size of scaffolds induced changes in cell adhesions and determined cell shape, spreading area, and extracellular matrix expression. In all, both mechanical property and topography features of scaffolds regulate AFSC differentiation, possibly through a YAP-dependent mechanotransduction mechanism. STATEMENT OF SIGNIFICANCE: Physical cues such as mechanical properties, topographical and geometrical features were shown to profoundly impact the growth and differentiation of cultured stem cells. Previously, we have found that the differentiation of annulus fibrosus-derived stem cells (AFSCs) could be regulated by the stiffness of scaffold. In this study, we fabricated four types of poly(ether carbonate urethane)urea (PECUU) scaffolds with controlled stiffness and fiber size to explore the potential of induced differentiation of AFSCs. We found that AFSCs are able to present different gene expression patterns simply as a result of the stiffness and fiber size of scaffold material. This work has, for the first time, demonstrated that larger-sized and higher-stiffness substrates increase the amount of vinculin assembly and activate YAP signaling in pre-differentiated AFSCs. The present study affords an in-depth comprehension of materiobiology, and be helpful for explain the mechanism of YAP mechanosensing in AF in response to biophysical effects of materials.

Efficiency of dual siRNA-mediated gene therapy for intervertebral disc degeneration (IVDD)

BACKGROUND CONTEXT

One of the common causes of low back pain is intervertebral disc degeneration. The pathophysiology of disc degeneration involves apoptosis of nucleus pulposes cells and degradation of extra cellular matrix (ECM). Caspase 3 plays a central role in apoptosis and the ADAMTS5 (A Disintegrin and Metalloproteinase with Thrombospondin motifs 5) gene plays a critical role in ECM degradation. Hence, we hypothesized that if one can silence these two genes, both apoptosis and ECM degradation can be prevented, thereby preventing the progression and even reverse disc degeneration.

PURPOSE

The purpose of this study is to demonstrate the regenerative potential of small interfering RNA (siRNA) designed against Caspase 3 and ADAMTS5 genes in an in vitro and animal model of disc degeneration.

STUDY DESIGN

In vitro study followed by in vivo study in a rabbit model.

METHODS

In vitro studies were done using the human hepatocellular carcinoma (Hep G2) cell line for validating the efficacy of liposomal siRNA in controlling the expression of genes (Caspase 3 and ADAMTS5). Later, siRNA's validation was done in a rabbit annular punctured model by administering siRNA's individually (Caspase 3 and ADAMTS5) and in combination Caspase3-ADAMTS5) for assessing their synergistic effect in down regulating the gene expression in the degenerative discs. Annular punctured intervertebral discs of the rabbit were injected with siRNA formulations (single and dual) and phosphate buffer saline, one week after initial puncture. Magnetic resonance imaging (MRI) scans were done before and after siRNA treatment (1, 4 and 8 weeks) for assessing the progression of disc degeneration. The histopathology and real time polymerase chain reaction (RT-PCR) studies were done for evaluating their efficacy. We did not receive any funding for conducting the study, and we do not have a conflict of interest with any researchers or scientific groups.

RESULTS

The observations made from both in vitro and in vivo studies indicate the beneficial effects of siRNA formulation in down regulating the expression of Caspase 3 and ADAMTS5 genes. The MRI and histopathological evaluation showed that the disc degeneration was progressive in phosphate buffer saline and AT5-siRNA injected discs but the discs that received Caspase 3-siRNA and dual siRNA (Cas3-AT5-siRNA) formulation showed signs of recovery and regeneration 4 and 8 weeks after injection. The efficacy of siRNA designed against Cas3 and AT5 was also assessed in both in vitro and in vivo experiments by using RT-PCR analysis and the results showed downregulation of Caspase 3 gene in Caspase 3-siRNA group, but there was no significant downregulation of ADAMTS5 gene in ADAMTS5-siRNA group (ie, indicated by fold change). Synergistic effect was observed in the group that received dual siRNA (Cas3-AT5 siRNA) formulation.

CONCLUSIONS

This experiment suggests that intervention by siRNA treatment significantly reduced the extent of apoptosis in the discs.

CLINICAL SIGNIFICANCE

Delivery of siRNA directly into spinal discs has a potential in treating disc degeneration nonsurgically.