Expression of neural and neurotrophic markers in nucleus pulposus cells isolated from degenerated intervertebral disc

Characterization of pain-related behaviors in a rat model of acute-to-chronic low back pain: single vs. multi-level disc injury

Introduction

Low back pain is the most common type of chronic pain. We examined pain-related behaviors across 18 weeks in rats that received injury to one or two lumbar intervertebral discs (IVD) to determine if multi-level disc injuries enhance/prolong pain.

Methods

Twenty-three Sprague-Dawley adult female rats were used: 8 received disc puncture (DP) of one lumbar IVD (L5/6, DP-1); 8 received DP of two lumbar IVDs (L4/5 & L5/6, DP-2); 8 underwent sham surgery.

Results

DP-2 rats showed local (low back) sensitivity to pressure at 6- and 12-weeks post-injury, and remote sensitivity to pressure (upper thighs) at 12- and 18-weeks and touch (hind paws) at 6, 12 and 18-weeks. DP-1 rats showed local and remote pressure sensitivity at 12-weeks only (and no tactile sensitivity), relative to Sham DP rats. Both DP groups showed reduced distance traveled during gait testing over multiple weeks, compared to pre-injury; only DP-2 rats showed reduced distance relative to Sham DP rats at 12-weeks. DP-2 rats displayed reduced positive interactions with a novel adult female rat at 3-weeks and hesitation and freezing during gait assays from 6-weeks onwards. At study end (18-weeks), radiological and histological analyses revealed reduced disc height and degeneration of punctured IVDs. Serum BDNF and TNFα levels were higher at 18-weeks in DP-2 rats, relative to Sham DP rats, and levels correlated positively with remote sensitivity in hind paws (tactile) and thighs (pressure).

Discussion

Thus, multi-level disc injuries resulted in earlier, prolonged and greater discomfort locally and remotely, than single-level disc injury. BDNF and TNFα may have contributing roles.

Alterations of bovine nucleus pulposus cells with aging

Aging is one of the major etiological factors driving intervertebral disc (IVD) degeneration, the main cause of low back pain. The nucleus pulposus (NP) includes a heterogeneous cell population, which is still poorly characterized. Here, we aimed to uncover main alterations in NP cells with aging. For that, bovine coccygeal discs from young (12 months) and old (10-16 years old) animals were dissected and primary NP cells were isolated. Gene expression and proteomics of fresh NP cells were performed. NP cells were labelled with propidium iodide and analysed by flow cytometry for the expression of CD29, CD44, CD45, CD146, GD2, Tie2, CD34 and Stro-1. Morphological cell features were also dissected by imaging flow cytometry. Elder NP cells (up-regulated bIL-6 and bMMP1 gene expression) presented lower percentages of CD29+, CD44+, CD45+ and Tie2+ cells compared with young NP cells (upregulated bIL-8, bCOL2A1 and bACAN gene expression), while GD2, CD146, Stro-1 and CD34 expression were maintained with age. NP cellulome showed an upregulation of proteins related to endoplasmic reticulum (ER) and melanosome independently of age, whereas proteins upregulated in elder NP cells were also associated with glycosylation and disulfide bonds. Flow cytometry analysis of NP cells disclosed the existence of 4 subpopulations with distinct auto-fluorescence and size with different dynamics along aging. Regarding cell morphology, aging increases NP cell area, diameter and vesicles. These results contribute to a better understanding of NP cells aging and highlighting potential anti-aging targets that can help to mitigate age-related disc disease.

Effects of the Co-Overexpression of the BCL and BDNF Genes on the Gamma-Aminobutyric Acid-Ergic Differentiation of Wharton's-Jelly-Derived Mesenchymal Stem Cells

One of the problems with using MSCs (mesenchymal stem cells) to treat different neurodegenerative diseases of the central nervous system is their low ability to spontaneously differentiate into functional neurons. The aim of this study was to investigate how the co-overexpression of the BCL and BDNF genes affects the ability of genetically modified MSCs to differentiate into GABA-ergic neurons. A co-overexpression of two genes was performed, one of which, BCL, was supposed to increase the resistance of the cells to the toxic agents in the brain environment. The second one, BDNF, was supposed to direct the cells onto the neuronal differentiation pathway. As a result, the co-overexpression of both BCL2 + BDNF and BCLXL + BDNF caused an increase in the MAP2 gene expression level (a marker of the neuronal pathway) and the SYP gene that is associated with synaptogenesis. In both cases, approximately 18% of the genetically modified and then differentiated cells exhibited the presence of the GAD protein, which is characteristic of GABA-ergic neurons. Despite the presence of GAD, after both modifications, only the BCL2 and BDNF co-overexpression correlated with the ability of the modified cells to release gamma-aminobutyric acid (GABA) after depolarization. Our study identified a novel model of genetically engineered MSCs that can be used as a tool to deliver the antiapoptotic proteins (BCL) and neurotrophic factor (BDNF) directly into the brain microenvironment. Additionally, in the investigated model, the genetically modified MSCs could easily differentiate into functional GABA-ergic neurons and, moreover, due to the secreted BCL and BDNF, promote endogenous neuronal growth and encourage synaptic connections between neurons.

Microgravity and the intervertebral disc: The impact of space conditions on the biomechanics of the spine

The environmental conditions to which astronauts and other military pilots are subjected represent a unique example for understanding and studying the biomechanical events that regulate the functioning of the human body. In particular, microgravity has shown a significant impact on various biological systems, such as the cardiovascular system, immune system, endocrine system, and, last but not least, musculoskeletal system. Among the potential risks of flying, low back pain (LBP) has a high incidence among astronauts and military pilots, and it is often associated with intervertebral disc degeneration events. The mechanisms of degeneration determine the loss of structural and functional integrity and are accompanied by the aberrant production of pro-inflammatory mediators that exacerbate the degenerative environment, contributing to the onset of pain. In the present work, the mechanisms of disc degeneration, the conditions of microgravity, and their association have been discussed in order to identify possible molecular mechanisms underlying disc degeneration and the related clinical manifestations in order to develop a model of prevention to maintain health and performance of air- and space-travelers. The focus on microgravity also allows the development of new proofs of concept with potential therapeutic implications.

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.

Intervertebral disc degeneration and how it leads to low back pain

The purpose of this review was to evaluate data generated by animal models of intervertebral disc (IVD) degeneration published in the last decade and show how this has made invaluable contributions to the identification of molecular events occurring in and contributing to pain generation. IVD degeneration and associated spinal pain is a complex multifactorial process, its complexity poses difficulties in the selection of the most appropriate therapeutic target to focus on of many potential candidates in the formulation of strategies to alleviate pain perception and to effect disc repair and regeneration and the prevention of associated neuropathic and nociceptive pain. Nerve ingrowth and increased numbers of nociceptors and mechanoreceptors in the degenerate IVD are mechanically stimulated in the biomechanically incompetent abnormally loaded degenerate IVD leading to increased generation of low back pain. Maintenance of a healthy IVD is, thus, an important preventative measure that warrants further investigation to preclude the generation of low back pain. Recent studies with growth and differentiation factor 6 in IVD puncture and multi-level IVD degeneration models and a rat xenograft radiculopathy pain model have shown it has considerable potential in the prevention of further deterioration in degenerate IVDs, has regenerative properties that promote recovery of normal IVD architectural functional organization and inhibits the generation of inflammatory mediators that lead to disc degeneration and the generation of low back pain. Human clinical trials are warranted and eagerly anticipated with this compound to assess its efficacy in the treatment of IVD degeneration and the prevention of the generation of low back pain.

The role of microenvironment in stem cell-based regeneration of intervertebral disc

Regenerative medicine for intervertebral disc (IVD) disease, by utilizing chondrocytes, IVD cells, and stem cells, has progressed to clinical trials in the treatment of back pain, and has been studied in various animal models of disc degeneration in the past decade. Stem cells exist in their natural microenvironment, which provides vital dynamic physical and chemical signals for their survival, proliferation and function. Long-term survival, function and fate of mesenchymal stem cells (MSCs) depend on the microenvironment in which they are transplanted. However, the transplanted MSCs and the endogenous disc cells were influenced by the complicated microenvironment in the degenerating disc with the changes of biochemical and biophysical components. It is important to understand how the MSCs and endogenous disc cells survive and thrive in the harsh microenvironment of the degenerative disc. Furthermore, materials containing stem cells and their natural microenvironment have good clinical effects. However, the implantation of tissue engineering IVD (TE-IVD) cannot provide a complete and dynamic microenvironment for MSCs. IVD graft substitutes may need further improvement to provide the best engineered MSC microenvironment. Additionally, the IVD progenitor cells inside the stem cell niches have been regarded as popular graft cells for IVD regeneration. However, it is still unclear whether actual IVD progenitor cells exist in degenerative spinal conditions. Therefore, the purpose of this review is fourfold: to discuss the presence of endogenous stem cells; to review and summarize the effects of the microenvironment in biological characteristics of MSC, especially those from IVD; to explore the feasibility and prospects of IVD graft substitutes and to elaborate state of the art in the use of MSC transplantation for IVD degeneration in vivo as well as their clinical application.

Extracellular vesicle and soluble fractions of adipose tissue-derived mesenchymal stem cells secretome induce inflammatory cytokines modulation in an in vitro model of discogenic pain

BACKGROUND CONTEXT

Mesenchymal stem cells (MSCs) secretome or conditioned medium (CM) is a complex cocktail of different molecules, some of which, particularly those contained in extracellular vesicles, already have proven therapeutic applications.

PURPOSE

CM may well represent promising therapy for discogenic pain and the intention of this work is to assess its therapeutic potential using an in vitro model of this condition.

STUDY DESIGN

This is an experimental study.

METHODS

Our in vitro model comprised nucleus pulposus (NP) and annulus fibrosus (AF) cells inflamed with TNF. To assess the potential therapeutic value of CM and its components, extracellular vesicles (EVs) and soluble culture fraction (SF), cell inflammation took place under 3 different conditions: either in the presence of whole CM, isolated EVs or SF, and concentrations of pro-inflammatory cytokines, metalloproteinases (MMPs) and neurotrophic factors produced in all 3 cases were compared.

RESULTS

In the presence of whole CM, both in vitro gene expression by the NP and AF test cells and analysis of their protein content showed high modulatory effects on inflammation and MMP inhibition. The presence of EVs and SF showed similar but much smaller effects, and this was particularly marked in the case of NP cells.

CONCLUSIONS

Our results show that, compared to EVs and SF, the presence of whole CM has the greatest positive effect on the modulation of pro-inflammatory and catabolic factors. These observations suggest that CM could protect against inflammation and the resulting intervertebral disc (IVD) degeneration that leads to discogenic pain.

CLINICAL SIGNIFICANCE

Many patients' expectations are not met by current non-operative and surgical treatments for discogenic low back pain. We propose the use of the MSCs secretome for assessing its potential as cell-free therapy to treat degenerative disc disease modulating the inflammatory response.

A Single Injection of NTG-101 Reduces the Expression of Pain-Related Neurotrophins in a Canine Model of Degenerative Disc Disease

Background: Tissue sources of pain emanating from degenerative discs remains incompletely understood. Canine intervertebral discs (IVDs) were needle puncture injured, 4-weeks later injected with either phosphate-buffered saline (PBS) or NTG-101, harvested after an additional fourteen weeks and then histologically evaluated for the expression of NGFr, BDNF, TrkB and CALCRL proteins. Quantification was performed using the HALO automated cell-counting scoring platform. Immunohistochemical analysis was also performed on human IVD tissue samples obtained from spinal surgery. Immunohistochemical analysis and quantification of neurotrophins and neuropeptides was performed using an in vivo canine model of degenerative disc disease and human degenerative disc tissue sections. Discs injected with NTG-101 showed significantly lower levels of Nerve Growth Factor receptor (NGFr/TrkA, p = 0.0001), BDNF (p = 0.009), TrkB (p = 0.002) and CALCRL (p = 0.008) relative to PBS injections. Human IVD tissue obtained from spinal surgery due to painful DDD show robust expression of NGFr, BDNF, TrkB and CALCRL proteins. A single intradiscal injection of NTG-101 significantly inhibits the expression of NGFr, BDNF, TrkB and CALCRL proteins in degenerative canine IVDs. These results strongly suggest that NTG-101 inhibits the development of neurotrophins that are strongly associated with painful degenerative disc disease and may have profound effects upon the management of patients living with discogenic pain.

Impact of Microenvironmental Changes during Degeneration on Intervertebral Disc Progenitor Cells: A Comparison with Mesenchymal Stem Cells

Intervertebral disc (IVD) degeneration occurs with natural ageing and is linked to low back pain, a common disease. As an avascular tissue, the microenvironment inside the IVD is harsh. During degeneration, the condition becomes even more compromised, presenting a significant challenge to the survival and function of the resident cells, as well as to any regeneration attempts using cell implantation. Mesenchymal stem cells (MSCs) have been proposed as a candidate stem cell tool for IVD regeneration. Recently, endogenous IVD progenitor cells have been identified inside the IVD, highlighting their potential for self-repair. IVD progenitor cells have properties similar to MSCs, with minor differences in potency and surface marker expression. Currently, it is unclear how IVD progenitor cells react to microenvironmental factors and in what ways they possibly behave differently to MSCs. Here, we first summarized the microenvironmental factors presented in the IVD and their changes during degeneration. Then, we analyzed the available studies on the responses of IVD progenitor cells and MSCs to these factors, and made comparisons between these two types of cells, when possible, in an attempt to achieve a clear understanding of the characteristics of IVD progenitor cells when compared to MSCs; as well as, to provide possible clues to cell fate after implantation, which may facilitate future manipulation and design of IVD regeneration studies.

Fundamentals of Intervertebral Disc Degeneration

Lumbar disc degeneration is one of the leading causes of chronic low back pain. The degenerative cascade is often initiated by an imbalance between catabolic and anabolic processes in the intervertebral discs. As a consequence of extracellular matrix degradation, neoinnervation and neovascularization take place. Ultimately, this degenerative process results in disc bulging and loss of nucleus pulposus and water content and subsequent loss of disc height. Most patients respond to conservative management and surgical interventions well initially, yet a significant number of patients continue to suffer from chronic low back pain. Because of the high prevalence of long-term discogenic pain, regenerative biological therapies, including gene therapies, growth factors, cellular-based injections, and tissue-engineered constructs, have attracted significant attention in light of their potential to directly address the degenerative process. Understanding the pathophysiology of degenerative disc disease is important in both refining existing technologies and developing innovative techniques to reverse the degenerative processes in the discs. In this review, we aimed to cover the underlying pathophysiology of degenerative disc disease as well as its associated risk factors and give a comprehensive summary about the developmental, structural, radiological, and biomechanical properties of human intervertebral discs.

Intervertebral Disc Stem/Progenitor Cells: A Promising "Seed" for Intervertebral Disc Regeneration

Intervertebral disc (IVD) degeneration is considered to be the primary reason for low back pain (LBP), which has become more prevalent from 21 century, causing an enormous economic burden for society. However, in spite of remarkable improvements in the basic research of IVD degeneration (IVDD), the effects of clinical treatments of IVDD are still leaving much to be desired. Accumulating evidence has proposed the existence of endogenous stem/progenitor cells in the IVD that possess the ability of proliferation and differentiation. However, few studies have reported the biological properties and potential application of IVD progenitor cells in detail. Even so, these stem/progenitor cells have been consumed as a promising cell source for the regeneration of damaged IVD. In this review, we will first introduce IVD, describe its physiology and stem/progenitor cell niche, and characterize IVDSPCs between homeostasis and IVD degeneration. We will then summarize recent studies on endogenous IVDSPC-based IVD regeneration and exogenous cell-based therapy for IVDD. Finally, we will discuss the potential applications and future developments of IVDSPC-based repair of IVD degeneration.

Pathomechanism and Biomechanics of Degenerative Disc Disease: Features of Healthy and Degenerated Discs

The human intervertebral disc (IVD) is a complex organ composed of fibrous and cartilaginous connective tissues, and it serves as a boundary between 2 adjacent vertebrae. It provides a limited range of motion in the torso as well as stability during axial compression, rotation, and bending. Adult IVDs have poor innate healing potential due to low vascularity and cellularity. Degenerative disc disease (DDD) generally arises from the disruption of the homeostasis maintained by the structures of the IVD, and genetic and environmental factors can accelerate the progression of the disease. Impaired cell metabolism due to pH alteration and poor nutrition may lead to autophagy and disruption of the homeostasis within the IVD and thus plays a key role in DDD etiology. To develop regenerative therapies for degenerated discs, future studies must aim to restore both anatomical and biomechanical properties of the IVDs. The objective of this review is to give a detailed overview about anatomical, radiological, and biomechanical features of the IVDs as well as discuss the structural and functional changes that occur during the degeneration process.

Current Progress in the Endogenous Repair of Intervertebral Disk Degeneration Based on Progenitor Cells

Intervertebral disk (IVD) degeneration is one of the most common musculoskeletal disease. Current clinical treatment paradigms for IVD degeneration cannot completely restore the structural and biomechanical functions of the IVD. Bio-therapeutic techniques focused on progenitor/stem cells, especially IVD progenitor cells, provide promising options for the treatment of IVD degeneration. Endogenous repair is an important self-repair mechanism in IVD that can allow the IVD to maintain a long-term homeostasis. The progenitor cells within IVD play a significant role in IVD endogenous repair. Improving the adverse microenvironment in degenerative IVD and promoting progenitor cell migration might be important strategies for implementation of the modulation of endogenous repair of IVD. Here, we not only reviewed the research status of treatment of degenerative IVD based on IVD progenitor cells, but also emphasized the concept of endogenous repair of IVD and discussed the potential new research direction of IVD endogenous repair.

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.

Involvement of the G-Protein-Coupled Receptor 4 in the Increased Expression of RANK/RANKL/OPG System and Neurotrophins by Nucleus Pulposus Cells under the Degenerated Intervertebral Disc-Like Acidic Microenvironment

Intervertebral disc (IVD) degeneration is associated with local inflammation and increased expression of neurotrophins. Acidic microenvironment is believed to cause the progression of IVD degeneration. However, there is a paucity of information regarding the relationship between acidic microenvironment and the inflammation and expression of neurotrophins in IVD. G-protein-coupled receptor 4 (GPR4) is a pH-sensing receptor, which can activate the inflammation and increase the expression levels of nerve growth factor in acidic microenvironment. In this study, culture media with pH 7.2 (representing the normal IVD-like acidic condition) and pH 6.5 (degenerated IVD-like acidic condition) were prepared. The gene and protein expression levels of GPR4 in SD rat nucleus pulposus cells were determined under the acidic conditions. And cyclic AMP (cAMP), the second messenger of GPR4, was assayed. Furthermore, the expression levels of receptor activator of nuclear factor κ B (RANK), RANKL ligand (RANKL), osteoprotegerin (OPG), nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) were also determined. To clarify the involvement of GPR4 in the upregulation of the expression of RANK/RANKL/OPG system and neurotrophins, gene knockdown and forced expression of GPR4 and inhibiting its downstream cAMP accumulation and Ca²⁺ mobilization were performed. The alternation of the expression levels of matrix metalloproteinase-3 (MMP-3), MMP-13, and aggrecanase-2 (ADAMTS-5) were evaluated by RT-PCR and western blot. The results showed that GPR4 was expressed in rat nucleus pulposus cells, and the expression was upregulated under the degenerated IVD-like acidic microenvironment. cAMP accumulation levels were increased under the degenerated IVD-like acidic culture conditions. The expression levels of RANK, RANKL, OPG, NGF, and BNDF were significantly upregulated under the degenerated IVD-like acidic microenvironment. GPR4 knockdown and reduction of cAMP by the inhibitor SQ22536 abolished the upregulation of the expression of RANK, RANKL, OPG, NGF, and BNDF under the degenerated IVD-like acidic microenvironment. On the opposite, acidosis-induced cAMP accumulation and upregulation of RANK, RANKL, OPG, NGF, and BNDF were further promoted by GPR4 overexpression. The expression levels of MMP-3, MMP-13, and ADAMTS-5 were upregulated under the degenerated IVD-like acidic condition, which can be promoted or attenuated by GPR4 overexpression or knockdown, respectively. We concluded that GPR4-mediated cAMP accumulation was involved in the increased expression of RANK/RANKL/OPG system and neurotrophins by nucleus pulposus cells under the degenerated IVD-like acidic microenvironment.

In vitro affinity optimization of an anti-BDNF monoclonal antibody translates to improved potency in targeting chronic pain states in vivo

The role of brain-derived neurotrophic factor (BDNF) signaling in chronic pain has been well documented. Given the important central role of BDNF in long term plasticity and memory, we sought to engineer a high affinity, peripherally-restricted monoclonal antibody against BDNF to modulate pain. BDNF shares 100% sequence homology across human and rodents; thus, we selected chickens as an alternative immune host for initial antibody generation. Here, we describe the affinity optimization of complementarity-determining region-grafted, chicken-derived R3bH01, an anti-BDNF antibody specifically blocking the TrkB receptor interaction. Antibody optimization led to the identification of B30, which has a > 300-fold improvement in affinity based on BIAcore, an 800-fold improvement in potency in a cell-based pERK assay and demonstrates exquisite selectivity over related neurotrophins. Affinity improvements measured in vitro translated to in vivo pharmacological activity, with B30 demonstrating a 30-fold improvement in potency over parental R3bH01 in a peripheral nerve injury model. We further demonstrate that peripheral BDNF plays a role in maintaining the plasticity of sensory neurons following nerve damage, with B30 reversing neuron hyperexcitability associated with heat and mechanical stimuli in a dose-dependent fashion. In summary, our data demonstrate that effective sequestration of BDNF via a high affinity neutralizing antibody has potential utility in modulating the pathophysiological mechanisms that drive chronic pain states.

IVD progenitor cells: a new horizon for understanding disc homeostasis and repair

Intervertebral disc (IVD) degeneration is associated with low back pain. In IVDs, a high mechanical load, high osmotic pressure and hypoxic conditions create a hostile microenvironment for resident cells. How IVD homeostasis and function are maintained under stress remains to be understood; however, several research groups have reported isolating native endogenous progenitor-like or otherwise proliferative cells from the IVD. The isolation of such cells implies that the IVD might contain a quiescent progenitor-like population that could be activated for IVD repair and regeneration. Increased understanding of endogenous disc progenitor cells will improve our knowledge of IVD homeostasis and, when combined with tissue engineering techniques, might hold promise for future therapeutic applications. In this Review, the characteristics of progenitor cells in different IVD compartments are discussed, as well as the potency of different cell populations within the IVD. The stem cell characteristics of these cells are also compared with those of mesenchymal stromal cells. On the basis of existing evidence, whether and how IVD degeneration and the hostile microenvironment might affect endogenous progenitor cell function are considered, and ways to channel the potential of these cells for IVD repair are suggested.

Characteristics and Potentiality of Human Adipose-Derived Stem Cells (hASCs) Obtained from Enzymatic Digestion of Fat Graft

Human adipose-derived stem cells localize in the stromal-vascular portion, and can be ex vivo isolated using a combination of washing steps and enzymatic digestion. For this study, we undertook a histological evaluation of traditional fat graft compared with fat graft enriched with stromal vascular fraction cells isolated by the Celution™ system to assess the interactions between cells and adipose tissue before the breast injection. In addition, we reported on histological analyses of biopsies derived from fat grafted (traditional or enriched with SVFs) in the breast in order to assess the quality of the adipose tissue, fibrosis and vessels. The hASCs derived from enzymatic digestion were systematically characterized for growth features, phenotype and multi-potent differentiation potential. They fulfill the definition of mesenchymal stem cells, albeit with a higher neural phenotype profile. These cells also express genes that constitute the core circuitry of self-renewal such as OCT4, SOX2, NANOG and neurogenic lineage genes such as NEUROD1, PAX6 and SOX3. Such findings support the hypothesis that hASCs may have a potential usefulness in neurodegenerative conditions. These data can be helpful for the development of new therapeutic approaches in personalized medicine to assess safety and efficacy of the breast reconstruction.

Molecular pain markers correlate with pH-sensitive MRI signal in a pig model of disc degeneration

Intervertebral disc (IVD) degeneration is a leading cause of chronic low back pain that affects millions of people every year. Yet identification of the specific IVD causing this pain is based on qualitative visual interpretation rather than objective findings. One possible approach to diagnosing pain-associated IVD could be to identify acidic IVDs, as decreased pH within an IVD has been postulated to mediate discogenic pain. We hypothesized that quantitative chemical exchange saturation transfer (qCEST) MRI could detect pH changes in IVDs, and thence be used to diagnose pathologically painful IVDs objectively and noninvasively. To test this hypothesis, a surgical model of IVD degeneration in Yucatan minipigs was used. Direct measurement of pH inside the degenerated IVDs revealed a significant drop in pH after degeneration, which correlated with a significant increase in the qCEST signal. Gene analysis of harvested degenerated IVDs revealed significant upregulation of pain-, nerve- and inflammatory-related markers after IVD degeneration. A strong positive correlation was observed between the expression of pain markers and the increase in the qCEST signal. Collectively, these findings suggest that this approach might be used to identify which IVD is causing low back pain, thereby providing valuable guidance for pain and surgical management.

Insight into neural mechanisms underlying discogenic back pain

Back pain is a common clinical symptom. Degeneration of intervertebral discs is one of the most important factors leading to back pain, namely, discogenic back pain. However, at present, the understanding of lumbar intervertebral discs causing back pain is confined to biomechanical and histological studies. The neuropathological mechanism related to discogenic back pain is still not well understood. Many studies have found that as an intervertebral disc degenerates, the peripheral nerve tissues have corresponding structural reorganization, and a series of nerve cells become involved in progression of discogenic back pain. Therefore, study of neural mechanisms that are involved in progression of discogenic back pain will provide additional assistance for treatment of its symptoms. We review the anatomical structure of intervertebral discs and the related neural mechanisms involved in discogenic back pain. We also discuss the current view of neural mechanisms underlying discogenic back pain.

Mechanical loading of intervertebral disc modulates microglia proliferation, activation, and chemotaxis

OBJECTIVE

The aim of the study is to assess the effects of the neuroinflammatory microenvironment of a mechanically-induced degenerating intervertebral disc (IVD) on neuroinflammatory like cells such as microglia, in order to comprehend the role of microglial cells in degenerative disc disease.

METHODS

Bovine caudal IVDs were kept in culture in an ex vivo bioreactor under high frequency loading and limited nutrition or in free swelling conditions as control samples. Conditioned media (CM) were collected, analysed for cytokine and neurotrophin content and applied to microglial cells for neuroinflammatory activation assessment.

RESULTS

Degenerative conditioned medium (D-CM) induced a higher production of interleukin (IL)-8, nerve growth factor (NGF), interferon (IFN)-γ, IL-17 from IVD cells than unloaded control conditioned medium (U-CM). Upon 48 h of co-incubation with microglia, D-CM stimulated microglia proliferation, activation, with increased expression of ionized calcium binding adaptor molecule 1 (IBA1) and CD68, and chemotaxis. Moreover, an increment of nitrite production was observed. Interestingly, D-CM caused an upregulation of IL-1β, IL-6, tumour necrosis factor α (TNFα), inducible NO synthase (iNOS), IBA1, and vascular endothelial growth factor (VEGF) genes in microglia. Similar results were obtained when microglia were treated with the combination of the measured cytokines.

CONCLUSIONS

Our findings show that in IVD degenerative microenvironment, IL-8, NGF, IFN-γ, IL-17 drive activation of microglia in the spinal cord and increase upregulation of neuroinflammatory markers. This, in turn, enhances the inflammatory milieu within IVD tissues and in the peridiscal space, aggravating the cascade of degenerative events. This study provides evidence for an important role of microglia in maintaining IVD neuroinflammatory microenvironment and probably inducing low back pain.

The Paracrine Effect of Degenerated Disc Cells on Healthy Human Nucleus Pulposus Cells Is Mediated by MAPK and NF-κB Pathways and Can Be Reduced by TGF-β1

Inflammation is thought to have a major role in the pathogenesis of disc degeneration. Studies have shown that nucleus pulposus cells (NPCs) respond to one or two specific cytokines by regulating cell proliferation or matrix synthesis. However, the effects of a cocktail of factors secreted by degenerated disc cells on transplanted exogenous healthy NPCs remain unknown. Concentrations of multiple cytokines in degenerated disc tissue-conditioned medium (dCM) were measured using enzyme-linked immunosorbent assay (ELISA). 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay and Ki67 immunofluorescence staining were used to evaluate the proliferation of cells in dCM. The function of exogenous NPCs cultured in dCM was evaluated by examining catabolic markers (ADAMTS-4, ADAMTS-5, MMP-1, MMP-3, and MMP-13), anabolic markers (TIMP-1, TIMP-2, and TIMP-3), and the extracellular matrix protein-aggrecan (ACAN) and collagen II (COL2)-expression with real time polymerase chain reaction (RT-PCR). Mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) pathway activation was observed using Western blotting. Finally, we examined the role of transforming growth factor (TGF)-β1 in reducing dCM-mediated exogenous NPC dysfunction. Levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-1α, IL-2, IL-4, IL-6, IL-8, IL-10, IL-17, interferon-γ (IFN-γ), and prostaglandin E2 (PGE2) were higher and TGF-β1 levels were lower in dCM compared with the control medium. Treatment with dCM increased the proliferation of healthy NPCs. NPCs exhibited significantly higher expression of ADAMTS-4, ADAMTS-5, MMP-1, MMP-3, and MMP-13 and decreased TIMP-2, ACAN, and COL2 expression in the dCM group in a dose- and time-dependent manner. Treatment with dCM moderately increased TIMP-1 expression and had no effect on TIMP-3 mRNA levels. The MAPK and NF-κB pathways were implicated in dCM-mediated responses of healthy NPCs. TGF-β1 partially reversed the dCM-mediated NPC dysfunction. Increased levels of inflammatory factors and decreased TGF-β1 levels in dCM suggest an inflammatory environment in degenerated disc tissue. The catabolic effect of dCM on human healthy NPCs is mediated by MAPK and NF-κB pathways and can be reduced by TGF-β1.

The Roles of Acidosis in Osteoclast Biology

The adverse effect of acidosis on the skeletal system has been recognized for almost a century. Although the underlying mechanism has not been fully elucidated, it appears that acidosis acts as a general stimulator of osteoclasts derived from bone marrow precursors cells and enhances osteoclastic resorption. Prior work suggests that acidosis plays a significant role in osteoclasts formation and activation via up-regulating various genes responsible for its adhesion, migration, survival and bone matrix degradation. Understanding the role of acidosis in osteoclast biology may lead to development of novel therapeutic approaches for the treatment of diseases related to low bone mass. In this review, we aim to discuss the recent investigations into the effects of acidosis in osteoclast biology and the acid-sensing molecular mechanism.

Class 3 semaphorins expression and association with innervation and angiogenesis within the degenerate human intervertebral disc

Nerve and blood vessel ingrowth during intervertebral disc degeneration, is thought to be a major cause of low back pain, however the regulation of this process is poorly understood. Here, we investigated the expression and regulation of a subclass of axonal guidance molecules known as the class 3 semaphorins, and their receptors; plexins and neuropilins within human NP tissue and their regulation by pro-inflammatory cytokines. Importantly this determined whether semaphorin expression was associated with the presence of nerves and blood vessels in tissues from human intervertebral discs. The study demonstrated that semaphorin3A, 3C, 3D, 3E and 3F and their receptors were expressed by native NP cells and further demonstrated their expression was regulated by IL-1β but to a lesser extent by IL-6 and TNFα. This is the first study to identify sema3C, sema3D and their receptors within the nucleus pulposus of intervertebral discs. Immunopositivity shows significant increases in semaphorin3C, 3D and their receptor neuropilin-2 in degenerate samples which were shown to contain nerves and blood vessels, compared to non-degenerate samples without nerves and blood vessels. Therefore data presented here suggests that semaphorin3C may have a role in promoting innervation and vascularisation during degeneration, which may go on to cause low back pain.

Stem Cell Approaches to Intervertebral Disc Regeneration: Obstacles from the Disc Microenvironment

Intervertebral disc (IVD) degeneration results in segmental instability and irritates neural compressive symptoms, such as low back pain and motor deficiency. The transplanting of stem cell into degenerative discs has attracted increasing clinical attention, as a new and proven approach to alleviating disc degeneration and to relieving discogenic pains. Aside from supplementation with stem cells, the IVD itself already contains a pool of stem and progenitor cells. Since the resident disc stem cells are incapable of reversing the pathologic changes that occur during aging and disc degeneration, it has been debated as to whether transplanted stem cells are capable of providing an efficient and durable therapeutic effect, even though there have been positive outcomes in both animal models and in clinical trials. This review aims to decipher the interactions between the stem cell and the disc microenvironment. Within their new niches in the IVD, the exogenous stem cell shows metabolic adaptation to the low-glucose supply, hypoxia, and compressive loadings, but demonstrates little tolerance to the disc-like acidity and hypertonicity. Similarly, the survival of endogenous stem cells is threatened as well by the harsh disc microenvironment, which may exhaust the stem cell resources and restrict the self-repair capacity of a degenerating IVD. To eliminate the intrinsic obstacles within the stressful disc niches, stem cells should be delivered with an injectable scaffold that provides both survival and mechanical support. Quick healing or concretion of the injection injuries, which minimizes stem cell leakage and disturbance to disc homeostasis, is of equal importance toward achieving efficient stem cell-based disc regeneration.

Characteristics and Properties of Mesenchymal Stem Cells Derived from Microfragmented Adipose Tissue

The subcutaneous adipose tissue provides a clear advantage over other mesenchymal stem cell sources due to the ease with which it can be accessed, as well as the ease of isolating the residing stem cells. Human adipose-derived stem cells (hADSCs), localized in the stromal–vascular portion, can be isolated ex vivo using a combination of washing steps and enzymatic digestion. In this study, we report that microfragmented human lipoaspirated adipose tissue is a better stem cell source compared to normal lipoaspirated tissue. The structural composition of microfragments is comparable to the original tissue. Differently, however, this procedure activates the expression of antigens, such as β-tubulin III. The hADSCs derived from microfragmented lipoaspirate tissue were systematically characterized for growth features, phenotype, and multipotent differentiation potential. They fulfill the definition of mesenchymal stem cells, although with a higher neural phenotype profile. These cells also express genes that constitute the core circuitry of self-renewal such as OCT4, SOX2, and NANOG, and neurogenic lineage genes such as NEUROD1, PAX6, and SOX3. Such findings suggest further studies by evaluating Microfrag-AT hADSC action in animal models of neurodegenerative conditions.

Theranostic impact of NG2/CSPG4 proteoglycan in cancer

NG2/CSPG4 is an unusual cell-membrane integral proteoglycan widely recognized to be a prognostic factor, a valuable tool for ex vivo and non-invasive molecular diagnostics and, by virtue of its tight association with malignancy, a tantalizing therapeutic target in several tumour types. Although the biology behind its involvement in cancer progression needs to be better understood, implementation of NG2/CSPG4 in the routine clinical practice is attainable and has the potential to contribute to an improved individualized management of cancer patients. In this context, its polymorphic nature seems to be particularly valuable in the effort to standardize informative diagnostic procedures and consolidate forcible immunotherapeutic treatment strategies. We discuss here the underpinnings for this potential and highlight the benefits of taking advantage of the intra-tumour and inter-patient variability in the regulation of NG2/CSPG4 expression. We envision that NG2/CSPG4 may effectively be exploited in therapeutic interventions aimed at averting resistance to target therapy agents and at interfering with secondary lesion formation and/or tumour recurrence.

Nucleus pulposus mesenchymal stem cells in acidic conditions mimicking degenerative intervertebral discs give better performance than adipose tissue-derived mesenchymal stem cells

The microenvironment of the intervertebral disc (IVD) is characterized by matrix acidity, hypoxia, hyperosmolarity and limited nutrition, which are major obstacles to stem cell-based regeneration. Our recent work showed that nucleus pulposus mesenchymal stem cells (NPMSCs) had advantages over traditional sources of cell therapy under IVD-like hypoxic and hyperosmotic conditions. Here, we examined the viability, proliferation and matrix metabolism of NPMSCs compared with adipose tissue-derived mesenchymal stem cells (ADMSCs) under IVD-like acidic conditions in vitro. ADMSCs and NPMSCs from Sprague-Dawley rats were cultured at four different pH levels representing the standard condition (pH 7.4) and the normal, mildly degenerated and severely degenerated IVD (pH 7.1, 6.8 and 6.5, respectively). Cell viability was examined by annexin-V-fluorescein isothiocyanate/propidium iodide staining. Cell proliferation was measured using a cell counting kit cell proliferation assay. The expression of aggrecan, collagen-I, collagen-II, matrix metalloproteinase-2 (MMP-2), a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS4) and the tissue inhibitor of metalloproteinase-3 (TIMP-3) was measured at mRNA and protein levels by RT-PCR and Western blotting. In both cell types, acidic pH inhibited cell viability and proliferation, downregulated the expression of aggrecan, collagen-I, collagen-II and TIMP-3, and upregulated the expression of MMP-2 and ADAMTS4. Compared with ADMSCs, NPMSCs were significantly less inhibited in viability and proliferation; they expressed significantly higher levels of aggrecan and collagen-II, and lower levels of MMP-2 and ADAMTS4. Thus, an acidic environment is a major obstacle for IVD regeneration by ADMSCs or NPMSCs. NPMSCs appeared less sensitive to inhibition by acidic pH and might be promising candidates for cell-based IVD regeneration.

Gene expression profile analysis of human mesenchymal stem cells from herniated and degenerated intervertebral discs reveals different expression of osteopontin

Gene expression analysis provides an effective methodology to identify clinically relevant genes implicated in intervertebral disc (IVD) pathology. The analysis of gene profile in mesenchymal stem cells (MSCs) from human herniated IVD (H-IVD) and degenerated IVD (D-IVD) has not yet been investigated. We present in this study a characterization of MSCs isolated from clinically categorized H-IVD and D-IVD disc samples. H-IVD-MSCs and D-IVD-MSCs showed multipotent mesenchymal differentiation ability, expressing positivity for adipogenic, osteogenic, and chondrogenic markers with an immunophenotypical profile representative of MSCs. FACS analyses revealed a higher expression of CD44 in D-IVD-MSCs compared to H-IVD-MSCs. Gene expression profile revealed that most genes under investigation displayed large variations and were not significantly different in the two types of analyzed IVD-MSCs. Conversely, the gene expression of osteopontin (OPN), a protein involved in bone matrix mineralization and extracellular matrix destruction, was found markedly increased (more than 400-fold) in D-IVD-MSCs compared to H-IVD-MSCs. Moreover, the OPN protein expression was detectable only in D-IVD-MSCs, and its levels were directly related with D-IVD severity. These findings suggest that an abnormal expression of OPN in D-IVD-MSCs occurs and plays a pivotal role in the pathophysiological process of human disc degeneration. We speculate that the regulation of the OPN pathway might be a therapeutic target to counteract disc degeneration.

Potential use of human adipose mesenchymal stromal cells for intervertebral disc regeneration: a preliminary study on biglycan-deficient murine model of chronic disc degeneration

INTRODUCTION

Biglycan is an important proteoglycan of the extracellular matrix of intervertebral disc (IVD), and its decrease with aging has been correlated with IVD degeneration. Biglycan deficient (Bgn-/0) mice lack this protein and undergo spontaneous IVD degeneration with aging, thus representing a valuable in vivo model for preliminary studies on therapies for human progressive IVD degeneration. The purpose of the present study was to assess the possible beneficial effects of adipose-derived stromal cells (ADSCs) implants in the Bgn-/0 mouse model.

METHODS

To evaluate ADSC implant efficacy, Bgn-/0 mice were intradiscally (L1-L2) injected with 8x104 ADSCs at 16 months old, when mice exhibit severe and complete IVD degeneration, evident on both 7Tesla Magnetic Resonance Imaging (7TMRI) and histology. Placebo and ADSCs treated Bgn-/0 mice were assessed by 7TMRI analysis up to 12 weeks post-transplantation. Mice were then sacrificed and implanted discs were analyzed by histology and immunohistochemistry for the presence of human cells and for the expression of biglycan and aggrecan in the IVD area.

RESULTS

After in vivo treatment, 7TMRI revealed evident increase in signal intensity within the discs of mice that received ADSCs, while placebo treatment did not show any variation. Ultrastructural analyses demonstrated that human ADSC survival occurred in the injected discs up to 12 weeks after implant. These cells acquired a positive expression for biglycan, and this proteoglycan was specifically localized in human cells. Moreover, ADSC treatment resulted in a significant increase of aggrecan tissue levels.

CONCLUSION

Overall, this work demonstrates that ADSC implant into degenerated disc of Bgn-/0 mice ameliorates disc damage, promotes new expression of biglycan and increased levels of aggrecan. This suggests a potential benefit of ADSC implant in the treatment of chronic degenerative disc disease and prompts further studies in this field.

Expression of acid-sensing ion channels in nucleus pulposus cells of the human intervertebral disk is regulated by non-steroid anti-inflammatory drugs

Non-steroid anti-inflammatory drugs (NSAIDs) are generally used in the treatment of inflammation and pain through cyclooxygenase (COX) inhibition. Mounting evidence has indicated additional COX-independent targets for NSAIDs including acid-sensing ion channels (ASICs) 1a and 3. However, detailed function and mechanism of ASICs still remain largely elusive. In this study, the impact of NSAIDs on ASICs in nucleus pulposus cells of the human intervertebral disk was investigated. Nucleus pulposus cells were isolated and cultured from protruded disk tissues of 40 patients. It was shown that ASIC1a and ASIC3 were expressed and functional in these cells by analyzing proton-gated currents after ASIC inhibition. We further investigated the neuroprotective capacity of ibuprofen (a COX inhibitor), psalmotoxin-1 (PcTX1, a tarantula toxin specific for homomeric ASIC1a), and amiloride (a classic inhibitor of the epithelial sodium channel ENaC/DEG family to which ASICs belong). PcTX1-containing venom has been shown to be comparable with amiloride in its neuroprotective features in rodent models of ischemia. Taken together, our data showed that amiloride, PcTX1, and ibuprofen decreased ASIC protein expression and thereby exerted protective effects from ASIC inhibition-mediated cell damage.

Expression and regulation of neurotrophic and angiogenic factors during human intervertebral disc degeneration

Introduction

The degenerate intervertebral disc (IVD) becomes innervated by sensory nerve fibres, and vascularised by blood vessels. This study aimed to identify neurotrophins, neuropeptides and angiogenic factors within native IVD tissue and to further investigate whether pro-inflammatory cytokines are involved in the regulation of expression levels within nucleus pulposus (NP) cells, nerve and endothelial cells.

Methods

Quantitative real-time PCR (qRT-PCR) was performed on 53 human IVDs from 52 individuals to investigate native gene expression of neurotrophic factors and their receptors, neuropeptides and angiogenic factors. The regulation of these factors by cytokines was investigated in NP cells in alginate culture, and nerve and endothelial cells in monolayer using RT-PCR and substance P (SP) protein expression in interleukin-1 (IL-1β) stimulated NP cells.

Results

Initial investigation on uncultured NP cells identified expression of all neurotrophins by native NP cells, whilst the nerve growth factor (NGF) receptor was only identified in severely degenerate and infiltrated discs, and brain derived neurotrophic factor (BDNF) receptor expressed by more degenerate discs. BDNF expression was significantly increased in infiltrated and degenerate samples. SP and vascular endothelial growth factor (VEGF) were higher in infiltrated samples. In vitro stimulation by IL-1β induced NGF in NP cells. Neurotropin-3 was induced by tumour necrosis factor alpha in human dermal microvascular endothelial cells (HDMECs). SP gene and protein expression was increased in NP cells by IL-1β. Calcitonin gene related peptide was increased in SH-SY5Y cells upon cytokine stimulation. VEGF was induced by IL-1β and interleukin-6 in NP cells, whilst pleiotrophin was decreased by IL-1β. VEGF and pleiotrophin were expressed by SH-SY5Y cells, and VEGF by HDMECs, but were not modulated by cytokines.

Conclusions

The release of cytokines, in particular IL-1β during IVD degeneration, induced significant increases in NGF and VEGF which could promote neuronal and vascular ingrowth. SP which is released into the matrix could potentially up regulate the production of matrix degrading enzymes and also sensitise nerves, resulting in nociceptive transmission and chronic low back pain. This suggests that IL-1β is a key regulatory cytokine, involved in the up regulation of factors involved in innervation and vascularisation of tissues.

Painful, degenerating intervertebral discs up-regulate neurite sprouting and CGRP through nociceptive factors

Intervertebral disc degeneration (IVD) can result in chronic low back pain, a common cause of morbidity and disability. Inflammation has been associated with IVD degeneration, however the relationship between inflammatory factors and chronic low back pain remains unclear. Furthermore, increased levels of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) are both associated with inflammation and chronic low back pain, but whether degenerating discs release sufficient concentrations of factors that induce nociceptor plasticity remains unclear. Degenerating IVDs from low back pain patients and healthy, painless IVDs from human organ donors were cultured ex vivo. Inflammatory and nociceptive factors released by IVDs into culture media were quantified by enzyme-linked immunosorbent assays and protein arrays. The ability of factors released to induce neurite growth and nociceptive neuropeptide production was investigated. Degenerating discs release increased levels of tumour necrosis factor-α, interleukin-1β, NGF and BDNF. Factors released by degenerating IVDs increased neurite growth and calcitonin gene-related peptide expression, both of which were blocked by anti-NGF treatment. Furthermore, protein arrays found increased levels of 20 inflammatory factors, many of which have nociceptive effects. Our results demonstrate that degenerating and painful human IVDs release increased levels of NGF, inflammatory and nociceptive factors ex vivo that induce neuronal plasticity and may actively diffuse to induce neo-innervation and pain in vivo.

Data mining for identifying novel associations and temporal relationships with Charcot foot

INTRODUCTION. Charcot foot is a rare and devastating complication of diabetes. While some risk factors are known, debate continues regarding etiology. Elucidating other associated disorders and their temporal occurrence could lead to a better understanding of its pathogenesis. We applied a large data mining approach to Charcot foot for elucidating novel associations. METHODS. We conducted an association analysis using ICD-9 diagnosis codes for every patient in our health system (n = 1.6 million with 41.2 million time-stamped ICD-9 codes). For the current analysis, we focused on the 388 patients with Charcot foot (ICD-9 713.5). RESULTS. We found 710 associations, 676 (95.2%) of which had a P value for the association less than 1.0 × 10⁻⁵ and 603 (84.9%) of which had an odds ratio > 5.0. There were 111 (15.6%) associations with a significant temporal relationship (P < 1.0 × 10⁻³). The three novel associations with the strongest temporal component were cardiac dysrhythmia, pulmonary eosinophilia, and volume depletion disorder. CONCLUSION. We identified novel associations with Charcot foot in the context of pathogenesis models that include neurotrophic, neurovascular, and microtraumatic factors mediated through inflammatory cytokines. Future work should focus on confirmatory analyses. These novel areas of investigation could lead to prevention or earlier diagnosis.

The role of leptin on the organization and expression of cytoskeleton elements in nucleus pulposus cells

Obesity is an important risk factor for intervertebral disc degeneration and leptin is a biomarker of obesity. However, the expression of leptin receptors has not been determined in disc tissue. It is not known whether leptin has a direct effect on the nucleus pulposus (NP) cells. To determine whether the NP tissues and cells express leptin receptors (OBRa and OBRb) and whether leptin affects the organization and the expression of major cytoskeletal elements in NP cells. Messenger RNA (mRNA) and protein levels of OBRa and OBRb were measured by real-time PCR and Western blot, respectively, in NP tissues and cells. Immunofluorescence and real-time PCR and Western blot were performed to investigate the effect of leptin on cytoskeleton reorganization and expression. Results show that mRNA and proteins of OBRa and OBRb were expressed in all NP tissues and cells, and that OBRb expression was correlated with patients' body weight. Increased expression of β-actin and reorganization of F-actin were evident in leptin-stimulated NP cells. Leptin also induced vimentin expression but had no effect on β-tubulin in NP cells. These findings provide novel evidence supporting the possible involvement of leptin in the pathogenesis of intervertebral disc degeneration.

Cell signaling pathways related to pain receptors in the degenerated disk

Many of the causes of low back pain are still unknown; sufficient evidence indicates that both degenerative and mechanical change within the intervertebral disk (IVD) is a relevant factor. This article reviews intracellular signaling pathways related to pain receptors in the degenerated IVD. Several reports have demonstrated the number of nerve fibers in the IVD was increased in degenerated disks. In recent years, some groups have reported that an increase in nerve fibers is associated with the presence of inflammatory mediators and/or neurotrophins in the IVD. Cell signaling events, which are regulated by inflammatory mediators and neurotrophins, must be identified to clarify the mechanism underlying low back pain. Major intracellular signaling pathways (nuclear factor kappa β, mitogen-activated protein kinases, and Wnts) potentially play vital roles in mediating the molecular events responsible for the initiation and progression of IVD degeneration. These signaling pathways may represent therapeutic targets for the treatment of IVD degeneration and its associated back pain.

Leptin induces cyclin D1 expression and proliferation of human nucleus pulposus cells via JAK/STAT, PI3K/Akt and MEK/ERK pathways

Increasing evidence suggests that obesity and aberrant proliferation of nucleus pulposus (NP) cells are associated with intervertebral disc degeneration. Leptin, a hormone with increased circulating level in obesity, has been shown to stimulate cell proliferation in a tissue-dependent manner. Nevertheless, the effect of leptin on the proliferation of human NP cells has not yet been demonstrated. Here, we show that leptin induced the proliferation of primary cultured human NP cells, which expressed the leptin receptors OBRa and OBRb. Induction of NP cell proliferation was confirmed by CCK8 assay and immunocytochemistry and Real-time PCR for PCNA and Ki-67. Mechanistically, leptin induced the phosphorylation of STAT3, Akt and ERK1/2 accompanied by the upregulation of cyclin D1. Pharmacological inhibition of JAK/STAT3, PI3K/Akt or MEK/ERK signaling by AG490, Wortmannin or U0126, respectively, reduced leptin-induced cyclin D1 expression and NP cell proliferation. These experiments also revealed an intricate crosstalk among these signaling pathways in mediating the action of leptin. Taken together, we show that leptin induces human NP cell cyclin D1 expression and proliferation via activation of JAK/STAT3, PI3K/Akt or MEK/ERK signaling. Our findings may provide a novel molecular mechanism that explains the association between obesity and intervertebral disc degeneration.