Accumulation and localization of macrophage phenotypes with human intervertebral disc degeneration

Differential Effector Response of Amnion- and Adipose-Derived Mesenchymal Stem Cells to Inflammation; Implications for Intradiscal Therapy

Intervertebral disc degeneration (IVDD) is a progressive condition marked by tissue destruction and inflammation. The therapeutic effector functions of mesenchymal stem cells (MSCs) makes them an attractive therapy for patients with IVDD. While several sources of MSCs exist, the optimal choice for use in the inflamed IVD remains a significant question. Adipose (AD)- and amnion (AM)-derived MSCs have several advantages compared with other sources, however, no study has directly compared the impact of IVDD inflammation on their effector functions. Human MSCs were cultured in media with or without supplementation of interleukin-1β (IL-1β) and tumor necrosis factor-α at concentrations reportedly produced by IVDD cells. MSC proliferation and production of pro- and anti-inflammatory cytokines were quantified following 24 and 48 h of culture. Additionally, the osteogenic and chondrogenic potential of AD- and AM-MSCs was characterized via histology and biochemical analysis following 28 days of culture. In inflammatory culture, AM-MSCs produced significantly more anti-inflammatory IL-10 (14.47 ± 2.39 pg/ml; p = 0.004) and larger chondrogenic pellets (5.67 ± 0.26 mm² ; p = 0.04) with greater percent area staining positively for glycosaminoglycan (82.03 ± 3.26%; p < 0.001) compared with AD-MSCs (0.00 ± 0.00 pg/ml; 2.76 ± 0.18 mm² ; 34.75 ± 2.49%; respectively). Conversely, AD-MSCs proliferated more resulting in higher cell numbers (221,000 ± 8,021 cells; p = 0.048) and produced higher concentrations of pro-inflammatory cytokines prostaglandin E₂ (1,118.30 ± 115.56 pg/ml; p = 0.030) and IL-1β (185.40 ± 7.63 pg/ml; p = 0.010) compared with AM-MSCs (109,667 ± 5,696 cells; 1,291.40 ± 78.47 pg/ml; 144.10 ± 4.57 pg/ml; respectively). AD-MSCs produced more mineralized extracellular matrix (3.34 ± 0.05 relative absorbance units [RAU]; p < 0.001) compared with AM-MSCs (1.08 ± 0.06 RAU). Under identical inflammatory conditions, a different effector response was observed with AM-MSCs producing more anti-inflammatories and demonstrating enhanced chondrogenesis compared with AD-MSCs, which produced more pro-inflammatory cytokines and demonstrated enhanced osteogenesis. These findings may begin to help inform researchers which MSC source may be optimal for IVD regeneration. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2445-2456, 2019.

Emerging Evidence of Macrophage Contribution to Hyperinnervation and Nociceptor Sensitization in Vulvodynia

Vulvodynia is an idiopathic chronic pain disorder and a leading cause of dyspareunia, or pain associated with sexual intercourse, for women. The key pathophysiological features of vulvodynia are vaginal hyperinnervation and nociceptor sensitization. These features have been described consistently by research groups over the past 30 years, but currently there is no first-line recommended treatment that targets this pathophysiology. Instead, psychological interventions, pelvic floor physiotherapy and surgery to remove painful tissue are recommended, as these are the few interventions that have shown some benefit in clinical trials. Recurrence of vulvodynia is frequent, even after vestibulectomy and questions regarding etiology remain. Vestibular biopsies from women with vulvodynia contain increased abundance of immune cells including macrophages as well as increased numbers of nerve fibers. Macrophages have multiple roles in the induction and resolution of inflammation and their function can be broadly described as pro-inflammatory or anti-inflammatory depending on their polarization state. This state is not fixed and can alter rapidly in response to the microenvironment. Essentially, M1, or classically activated macrophages, produce pro-inflammatory cytokines and promote nociceptor sensitization and mechanical allodynia, whereas M2, or alternatively activated macrophages produce anti-inflammatory cytokines and promote functions such as wound healing. Signaling between macrophages and neurons has been shown to promote axonal sprouting and nociceptor sensitization. This mini review considers emerging evidence that macrophages may play a role in nociceptor sensitization and hyperinnervation relevant to vulvodynia and considers the implications for development of new therapeutic strategies.

Changes in Nerve Growth Factor Expression and Macrophage Phenotype Following Intervertebral Disc Injury in Mice

Nerve growth factor (NGF) is increased in intervertebral discs (IVDs) after disc injury and anti-NGF therapy improves low back pain in humans. Furthermore, M1 and M2 macrophage subtypes play a role in degenerative IVD injury. We examined M1 and M2 macrophage markers and NGF and cytokine expression in IVD-derived cells from control and IVD-injured mice for 28 days following injury. Ngf messenger RNA (mRNA) expression was increased 1 day after injury in injured compared with control mice, and persisted for up to 28 days. Flow cytometric analysis demonstrated that the proportion of F4/80+ CD11b+ cells was significantly increased from 1 day after injury for up to 28 days in injured compared to control mice. mRNA expression of M1 macrophage markers Tnfa, Il1b, and Nos2 was significantly increased 1 day after injury in injured compared to control mice, before gradually decreasing. At 28 days, no significant difference was observed in M1 markers. The M2a marker, Ym1, was significantly increased 1 day after injury in injured compared with control mice, while M2a and M2c markers Tgfb and Cd206 were significantly increased 7, 14, and 28 days after injury. Tumor necrosis factor α (TNF-α) and transforming growth factor β (TGF-β) stimulated Ngf mRNA and NGF protein expression in IVD cells. Our results suggest that TNF-α and TGF-β may stimulate NGF production under inflammatory and non-inflammatory conditions following IVD injury. As TNF-α and TGF-β are produced by M1 and M2 macrophages, further investigations are needed to reveal the role of macrophages in NGF expression following IVD injury. Our results may aid in developing treatments for IVD-related LBP pathology. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1798-1804, 2019.

Mast Cell/Proteinase Activated Receptor 2 (PAR2) Mediated Interactions in the Pathogenesis of Discogenic Back Pain

Mast cells (MCs) are present in the painful degenerate human intervertebral disc (IVD) and are associated with disease pathogenesis. MCs release granules containing enzymatic and inflammatory factors in response to stimulants or allergens. The serine protease, tryptase, is unique to MCs and its activation of the G-protein coupled receptor, Protease Activated Receptor 2 (PAR2), induces inflammation and degradation in osteoarthritic cartilage. Our previously published work has demonstrated increased levels of MC marker tryptase in IVD samples from discogenic back pain patients compared to healthy control IVD samples including expression of chemotactic agents that may facilitate MC migration into the IVD. To further elucidate MCs’ role in the IVD and mechanisms underlying its effects, we investigated whether (1) human IVD cells can promote MC migration, (2) MC tryptase can mediate up-regulation of inflammatory/catabolic process in human IVD cells and tissue, and (3) the potential of PAR2 antagonist to function as a therapeutic drug in in vitro human and ex vivo bovine pilot models of disease. MC migration was quantitatively assessed using conditioned media from primary human IVD cells and MC migration examined through Matrigel. Exposure to soluble IVD factors significantly enhanced MC migration, suggesting IVD cells can recruit MCs. We also demonstrated significant upregulation of MC chemokine SCF and angiogenic factor VEGFA gene expression in human IVD cells in vitro in response to recombinant human tryptase, suggesting tryptase can enhance recruitment of MCs and promotion of angiogenesis into the usually avascular IVD. Furthermore, tryptase can degrade proteoglycans in IVD tissue as demonstrated by significant increases in glycosaminoglycans released into surrounding media. This can create a catabolic microenvironment compromising structural integrity and facilitating vascular migration usually inhibited by the anti-angiogenic IVD matrix. Finally, as a “proof of concept” study, we examined the therapeutic potential of PAR2 antagonist (PAR2A) on human IVD cells and bovine organ culture IVD model. While preliminary data shows promise and points toward structural restoration of the bovine IVD including down-regulation of VEGFA, effects of PAR2 antagonist on human IVD cells differ between gender and donors suggesting that further validation is required with larger cohorts of human specimens.

Macrophages Down-Regulate Gene Expression of Intervertebral Disc Degenerative Markers Under a Pro-inflammatory Microenvironment

Low back pain is a highly prevalent clinical problem and intervertebral disc (IVD) degeneration is now accepted as the major pathophysiological mechanism responsible for this condition. Accumulating evidence suggests that inflammation plays a crucial role in the progression of human IVD degeneration, with macrophages being pointed as the key immune cell players in this process since their infiltration in degenerated IVD samples has been extensively demonstrated. Since they are highly plastic, macrophages can play different roles depending on the microenvironmental cues. The study of inflammation associated with IVD degeneration has been somehow neglected and one of the reasons is related with lack of adequate models. To overcome this, we established and characterized a new model of IVD organ culture under pro-inflammatory conditions to further dissect the role of macrophages in IVD associated immune response. For that, human monocyte-derived macrophages were co-cultured either with bovine caudal IVD punches in the presence of the pro-inflammatory cytokine IL-1β, or IVD-conditioned medium (CM), to investigate how IVD-produced factors influence macrophage phenotype. After 72 h, metabolic activity, gene expression and cytokine profile of macrophages and IVD cells were measured. Our results show that macrophages and IVDs remain metabolically active in the presence of IL-1β, significantly upregulate CCR7 gene expression and increase production of IL-6 on macrophages. When treating macrophages with IL-1β-IVD-CM, CCR7 upregulation follows the same trend, while for IL-6 an opposite effect was observed. On the other hand, macrophages interfere with IVD ECM remodeling, decreasing MMP3 expression and downregulating aggrecan and collagen II gene expression in the presence of IL-1β. Overall, the co-culture model established in this study can be considered a suitable approach to address the cellular and molecular pathways that regulate macrophage-IVD crosstalk, suggesting that degenerated IVD tissue tends to polarize human macrophages toward a more pro-inflammatory profile, which seems to aggravate IVD degeneration. This model could be used to improve the knowledge of the mechanisms that link IVD degeneration and the immune response.

Secreted Factors From Intervertebral Disc Cells and Infiltrating Macrophages Promote Degenerated Intervertebral Disc Catabolism

STUDY DESIGN

Rat nucleus pulposus (NP) cells or annulus fibrosus (AF) cells were stimulated with conditioned media of RAW 264.7 macrophages and vice versa under healthy culture conditions and in the presence of pro-inflammatory mediators. The gene expression of pro-inflammatory mediators, extracellular matrix (ECM)-modifying enzymes, and chemokines, which play important roles in intervertebral disc degeneration (IDD), was determined.

OBJECTIVE

To test whether the interaction between native disc cells and infiltrating macrophages accelerates inflammation state, disrupts matrix homeostasis, and promotes inflammatory cells infiltration.

SUMMARY OF BACKGROUND DATA

With macrophages infiltration, the disc resident cells would be inevitably exposed to macrophages. Macrophages have been shown to play pro-inflammatory role in the cellular interactions with disc cells under healthy culture conditions. However, the biologic interactions between macrophages and disc cells under degenerated disc inflammatory environment remain unknown.

METHODS

Murine Macrophages RAW 264.7 were cultured in the conditioned media of Rat AF or NP cells culture in the presence or absence of IL-1β stimulation. Similarly, Rat AF or NP cells were also cultured in the conditioned media of Murine Macrophages RAW 264.7 culture in the presence or absence of IFN-γ stimulation. The mRNA levels difference of pro-inflammatory genes, catabolic genes and chemokines genes for AF cells, NP cells and Macrophages RAW 264.7 were analyzed by qRT-PCR, respectively.

RESULTS

Compared with serum-free media exposure, RAW 264.7 macrophages exposed to AF or NP cells conditioned media selectively modestly upregulated mRNA levels of the aforementioned cytokines. Exposure of RAW 264.7 macrophages to conditioned media from AF or NP cells with IL-1β stimulation dramatically increased mRNA levels of all the investigated cytokines. Similarly, compared with serum-free media exposure, AF or NP cells exposed to RAW 264.7 macrophages conditioned media selectively modestly upregulated mRNA levels of the aforementioned cytokines. Exposure of AF or NP cells to conditioned media from RAW 264.7 macrophages with IFN-γ stimulation dramatically increased mRNA levels of all the investigated cytokines.

CONCLUSION

The biologic interactions between infiltrating macrophages and native disc cells under degenerated disc inflammatory environment lead to an increasingly severe inflammatory conditions, which may be a self-stimulated process from the macrophages infiltration occurrenceLevel of Evidence: 5.

Characterization of neuroinflammation and periphery-to-CNS inflammatory cross-talk in patients with disc herniation and degenerative disc disease

The aim of the study was to identify inflammatory cytokines/chemokines associated with neuroinflammation and periphery-to-CNS inflammatory cross-talk in degenerative disc disease (DDD) and lumbar disc herniation (LDH), common causes of low back pain (LBP). A secondary aim was to investigate the associations between cytokines and symptom severity.

METHODS

In total, 40 DDD and 40 LDH patients were recruited from a surgical waiting list, as well as 39 healthy controls (HC) and 40 cerebrospinal fluid (CSF) controls. The subjects completed questionnaires and pressure algometry was performed at the lumbar spine and forearm. The CSF, serum and disc tissues were collected during surgery. Inflammatory mediators TNF, INFg, IL-1b, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p70, IL-13 and MCP1 were analysed by immunoassay (Meso Scale Discovery) and quantitative real-time polymerase chain reaction (qPCR) was used for analysis of IL-6, IL-8, MCP1 and TSPO expression in intervertebral discs (IVDs).

RESULTS

In the LDH group, we found elevated IL-8 concentrations in CSF indicating neuroinflammation, while IL-8 and MCP1 concentrations in serum were lower compared to HC. The IVD expression of IL-6, IL-8 and TSPO was lower in LDH patients compared to DDD. LDH patients had a positive correlation between IL-8 concentrations in CSF and serum and IL-8 in CSF was associated with higher pain intensity and increased spinal pressure pain sensitivity. The MCP1 concentration in serum was associated with higher global pain ratings and increased spinal pressure pain sensitivity, while IL-6 serum concentration correlated with the intensity of the neuropathic pain component (leg pain) in LDH patients. IVD expression of TSPO in LDH patients was associated with increased intensity of back pain. No differences were found in cytokine CSF concentrations between DDD patients and CSF controls, but DDD patients had lower IL-8 and MCP1 serum concentrations than HC. In female DDD patients, IL-8 and MCP1 concentrations in serum were associated with increased intensity of back pain.

CONCLUSION

Our results suggest that neuroinflammation mediated by elevated IL-8 concentrations in CSF and IL-8 mediated periphery-to-CNS inflammatory cross-talk contributes to pain in LDH patients and suggest a link between TSPO expression in discs and low back pain.

Proinflammatory macrophages promote degenerative phenotypes in rat nucleus pulpous cells partly through ERK and JNK signaling

Intervertebral disc (IVD) degeneration is the major contributor to low back pain, a highly prevalent musculoskeletal problem that represents the leading cause of disability. Proinflammatory M1 macrophages were identified in degenerated IVDs. However, their role in the pathogenesis of IVD degeneration and the underlying mechanism was largely unknown. In this study, we explored the combined effects of molecules secreted by M1 macrophages on nucleus pulposus cells, by treating rat nucleus pulposus cells (rNP) with the conditioned medium collected from M1-polarized RAW264.7 cells (MФCM). We found that MФCM caused molecular changes associated with IVD degeneration, including increased expression of key matrix catabolic genes (Adamts4, Adamts5, Mmp3, and Mmp13), reduced the expression of major matrix-associated anabolic genes ( Sox9, Acan, and Col2a1), and upregulated transcription of inflammation-related genes ( IL-1b, IL-6, Ccl2, and Ccl3), in rNP cells. Moreover, we found that MФCM activated both ERK and JNK pathways in these cells, and that inhibition of JNK pathway attenuated MФCM-induced expression of both catabolic and inflammatory genes, whereas ERK inhibition only suppressed induction of catabolic, but not inflammatory genes. Together, our data demonstrated that proinflammatory macrophages promoted the degenerative phenotypes in rNP cells in part through ERK and JNK signaling, and suggested that inhibition of these pathways may serve as a potential therapeutic approach for the treatment of IVD degeneration.

Annulus fibrosus cell phenotypes in homeostasis and injury: implications for regenerative strategies

Despite considerable efforts to develop cellular, molecular, and structural repair strategies and restore intervertebral disk function after injury, the basic biology underlying intervertebral disk healing remains poorly understood. Remarkably, little is known about the origins of cell populations residing within the annulus fibrosus, or their phenotypes, heterogeneity, and roles during healing. This review focuses on recent literature highlighting the intrinsic and extrinsic cell types of the annulus fibrosus in the context of the injury and healing environment. Spatial, morphological, functional, and transcriptional signatures of annulus fibrosus cells are reviewed, including inner and outer annulus fibrosus cells, which we propose to be referred to as annulocytes. The annulus also contains peripheral cells, interlamellar cells, and potential resident stem/progenitor cells, as well as macrophages, T lymphocytes, and mast cells following injury. Phases of annulus fibrosus healing include inflammation and recruitment of immune cells, cell proliferation, granulation tissue formation, and matrix remodeling. However, annulus fibrosus healing commonly involves limited remodeling, with granulation tissues remaining, and the development of chronic inflammatory states. Identifying annulus fibrosus cell phenotypes during health, injury, and degeneration will inform reparative regeneration strategies aimed at improving annulus fibrosus healing.

Neonatal mouse intervertebral discs heal with restored function following herniation injury

Adult intervertebral discs (IVDs) have poor endogenous healing capacity, because of their challenging microenvironment and complex mechanical demands, which can result in painful IVD herniation. There are no regenerative strategies available to improve IVD healing and restore its function. Neonatal mice are excellent models of mammalian regeneration, but there are no studies of the regenerative capacity of neonatal IVDs. In this study, we developed a neonatal model of improved IVD healing to inform repair strategies after herniation. In vivo puncture injuries were performed to simulate herniation with complete annulus fibrosus (AF) tears in caudal IVDs of neonatal (postnatal d 5) and adult (4-6 mo) Scleraxis green fluorescent protein ( ScxGFP) mice. Acute and long-term healing responses were assessed with histologic, radiologic, and biomechanical measurements. Neonates underwent accelerated IVD healing compared to adults with functional restoration and enhanced structural repair after herniation. A population of ScxGFP- cells identified in the neonatal repair site may be associated with this improved healing and warrants future investigation. In summary, function of neonatal IVDs was restored after herniation injury, whereas that of adult discs was not. This improved healing response is likely driven by multiple mechanisms that may include differences in mechanical loading and available repair cells during growth.-Torre, O. M., Das, R., Berenblum, R. E., Huang, A. H., Iatridis, J. C. Neonatal mouse intervertebral discs heal with restored function following herniation injury.

Effect of Thrombin-Induced MCP-1 and MMP-3 Production Via PAR1 Expression in Murine Intervertebral Discs

Structural changes in nucleus pulposus cells induce intervertebral disc (IVD) degeneration as a consequence of cytokine generation, biochemical products, and changes in the local environment. We have previously shown that inflammatory cytokines induce murine IVD (mIVD) angiogenesis and macrophage migration. Although the physiological roles of thrombin, a known proinflammatory factor, are documented, its relationship to IVD degeneration remains largely unexplored. Thrombin mediates cellular responses via the activation of protease-activated receptors such as PAR1 which has been studied in numerous cell types, but not extensively in IVD cells. This study was designed to investigate the endogenous expression of thrombin, tissue factor, and PAR1 in cultured coccygeal mIVDs. Thrombin exclusively induced MCP-1 via the MAPK-ERK and PI3K-AKT pathways. MCP-1 produced by mIVDs induced macrophage migration and thrombin treatment increased MMP-3 production to induce mIVD degeneration. These effects of thrombin on mIVDs were abrogated by a PAR1 inhibitor and suggest that thrombin may be a novel factor capable of stimulating cytokine activity implicated in the regulation several aspects of mIVDs. Mechanisms governing mIVDs, which are regulated by thrombin/PAR1 signaling, require elucidation if our understanding of IVD degenerative mechanisms is to advance.

Inhibiting tumor necrosis factor-alpha at time of induced intervertebral disc injury limits long-term pain and degeneration in a rat model

Background

Painful intervertebral disc (IVD) degeneration has tremendous societal costs and few effective therapies. Intradiscal tumor necrosis factor‐alpha (TNFα) is commonly associated with low back pain, but the direct relationship remains unclear.

Purpose

Treatment strategies for low back pain require improved understanding of the complex relationships between pain, intradiscal pro‐inflammatory cytokines, and structural IVD degeneration. A rat in vivo lumbar IVD puncture model was used to 1) determine the role of TNFα in initiating painful IVD degeneration, and 2) identify statistical relationships between painful behavior, IVD degeneration, and intradiscal pro‐inflammatory cytokine expression.

Methods

Lumbar IVDs were punctured anteriorly and injected with TNFα, anti‐TNFα, or saline and compared with sham and naive controls. Hindpaw mechanical hyperalgesia was assayed weekly to determine pain over time. 6‐weeks post‐surgery, animals were sacrificed, and IVD degeneration, IVD height, and intradiscal TNFα and interleukin‐1 beta (IL‐1β) expressions were assayed.

Results

Intradiscal TNFα injection increased pain and IVD degeneration whereas anti‐TNFα alleviated pain to sham level. Multivariate step‐wise linear regression identified pain threshold was predicted by IVD degeneration and intradiscal TNFα expression. Pain threshold was also linearly associated with IVD height loss and IL‐1β.

Discussion

The significant associations between IVD degeneration, height loss, inflammation, and painful behavior highlight the multifactorial nature of painful IVD degeneration and the challenges to diagnose and treat a specific underlying factor. We concluded that TNFα is an initiator of painful IVD degeneration and its early inhibition can mitigate pain and degeneration. Intradiscal TNFα inhibition following IVD injury may warrant investigation for its potential to alter downstream painful IVD degeneration processes.

Macrophage-derived inflammatory cytokines regulate growth factors and pain-related molecules in mice with intervertebral disc injury

Upregulation of inflammatory cytokines and various growth factors is a significant contributor to discogenic low back pain. The aim of this study was to investigate possible regulation of pain-related molecules by macrophages and the role of macrophage-derived molecules in injured intervertebral disc (IVD)s. C57BL/6J mice were used in this study. We characterized the expression profiles of genes for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, nerve growth factor (NGF), and vascular endothelial growth factor (VEGF) in both intact and injured IVDs. We examined whether macrophage depletion, induced by systemic injection of clodronate-laden liposomes, affected the expression of these molecules in injured IVDs. The effect of TNF-alpha on cultured F4/80-CD11b-cells in injured IVDs was investigated. Expression of TNF-alpha and IL-1beta was significantly increased in injured IVDs, but decreased by macrophage depletion. Expression of NGF and VEGF was also significantly increased, but by contrast was not decreased by macrophage depletion. TNF-alpha treatment of F4/80-cells from injured IVDs upregulated NGF, VEGF, cyclooxygenase (COX)-2, and microsomal prostaglandin E synthase-1 (mPGES1). IVD injury upregulated inflammatory cytokines and various growth factors. Macrophages in the injured IVDs produced inflammatory cytokines, but not growth factors. Macrophage-derived inflammatory cytokines regulate growth factors and pain-related molecules. These findings demonstrate further complexity in the pathogenesis of discogenic pain. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.