HSP90 Inhibitor 17-AAG Attenuates Nucleus Pulposus Inflammation and Catabolism Induced by M1-Polarized Macrophages

Role of macrophage in intervertebral disc degeneration

Intervertebral disc degeneration is a degenerative disease where inflammation and immune responses play significant roles. Macrophages, as key immune cells, critically regulate inflammation through polarization into different phenotypes. In recent years, the role of macrophages in inflammation-related degenerative diseases, such as intervertebral disc degeneration, has been increasingly recognized. Macrophages construct the inflammatory microenvironment of the intervertebral disc and are involved in regulating intervertebral disc cell activities, extracellular matrix metabolism, intervertebral disc vascularization, and innervation, profoundly influencing the progression of disc degeneration. To gain a deeper understanding of the inflammatory microenvironment of intervertebral disc degeneration, this review will summarize the role of macrophages in the pathological process of intervertebral disc degeneration, analyze the regulatory mechanisms involving macrophages, and review therapeutic strategies targeting macrophage modulation for the treatment of intervertebral disc degeneration. These insights will be valuable for the treatment and research directions of intervertebral disc degeneration.

The Role of Microvascular Variations in the Process of Intervertebral Disk Degeneration and Its Regulatory Mechanisms: A Literature Review

Microvascular changes are considered key factors in the process of intervertebral disk degeneration (IDD). Microvascular invasion and growth into the nucleus pulposus (NP) and cartilaginous endplates are unfavorable factors that trigger IDD. In contrast, the rich distribution of microvessels in the bony endplates and outer layers of the annulus fibrosus is an important safeguard for the nutrient supply and metabolism of the intervertebral disk (IVD). In particular, the adequate supply of microvessels in the bony endplates is the main source of the nutritional supply for the entire IVD. Microvessels can affect the progression of IDD through a variety of pathways. Many studies have explored the effects of microvessel alterations in the NP, annulus fibrosus, cartilaginous endplates, and bony endplates on the local microenvironment through inflammation, apoptosis, and senescence. Studies also elucidated the important roles of microvessel alterations in the process of IDD, as well as conducted in-depth explorations of cytokines and biologics that can inhibit or promote the ingrowth of microvessels. Therefore, the present manuscript reviews the published literature on the effects of microvascular changes on IVD to summarize the roles of microvessels in IVD and elaborate on the mechanisms of action that promote or inhibit de novo microvessel formation in IVD.

LTF ameliorates cartilage endplate degeneration by suppressing calcification, senescence and matrix degradation through the JAK2/STAT3 pathway

Intervertebral disc degeneration (IDD)-induced cervical and lumbar herniations are debilitating diseases. The function of intervertebral disc (IVD) mainly depends on the cartilage endplate (CEP), which provides support and waste removal. Therefore, IDD stems from the degeneration of CEP. Our study shows that the expression of lactotransferrin (LTF), an iron-binding protein, is significantly decreased in degenerated human and rat CEP tissues. In addition, we found that LTF knockdown promoted calcification, senescence, and extracellular matrix (ECM) degradation in human endplate chondrocytes. Furthermore, the in vivo experiment results confirmed that the JAK2/STAT3 pathway inhibitor AG490 significantly reversed these effects. In addition to investigating the role and mechanism of LTF in CEP degeneration, this study provides a theoretical basis and experimental evidence to improve IDD treatment.

Osteopontin deficiency promotes cartilaginous endplate degeneration by enhancing the NF-κB signaling to recruit macrophages and activate the NLRP3 inflammasome

Intervertebral disc degeneration (IDD) is a major cause of discogenic pain, and is attributed to the dysfunction of nucleus pulposus, annulus fibrosus, and cartilaginous endplate (CEP). Osteopontin (OPN), a glycoprotein, is highly expressed in the CEP. However, little is known on how OPN regulates CEP homeostasis and degeneration, contributing to the pathogenesis of IDD. Here, we investigate the roles of OPN in CEP degeneration in a mouse IDD model induced by lumbar spine instability and its impact on the degeneration of endplate chondrocytes (EPCs) under pathological conditions. OPN is mainly expressed in the CEP and decreases with degeneration in mice and human patients with severe IDD. Conditional Spp1 knockout in EPCs of adult mice enhances age-related CEP degeneration and accelerates CEP remodeling during IDD. Mechanistically, OPN deficiency increases CCL2 and CCL5 production in EPCs to recruit macrophages and enhances the activation of NLRP3 inflammasome and NF-κB signaling by facilitating assembly of IRAK1-TRAF6 complex, deteriorating CEP degeneration in a spatiotemporal pattern. More importantly, pharmacological inhibition of the NF-κB/NLRP3 axis attenuates CEP degeneration in OPN-deficient IDD mice. Overall, this study highlights the importance of OPN in maintaining CEP and disc homeostasis, and proposes a promising therapeutic strategy for IDD by targeting the NF-κB/NLRP3 axis.

AMPK Regulates M1 Macrophage Polarization through the JAK2/STAT3 Signaling Pathway to Attenuate Airway Inflammation in Obesity-Related Asthma

Abstract-Obesity-related asthma is primarily characterized by nonallergic inflammation, with pathogenesis involving oxidative stress, metabolic imbalance, and immunoinflammatory mechanisms. M1 macrophages, which predominantly secrete pro-inflammatory factors, mediate insulin resistance and systemic metabolic inflammation in obese individuals. Concurrently, adenosine monophosphate-activated protein kinase (AMPK) serves as a critical regulator of intracellular energy metabolism and is closely associated with macrophage activation. However, their specific roles and associated mechanisms in obesity-related asthma remain to be explored. In this study, we investigated the macrophage polarization status and potential interventional mechanisms through obesity-related asthmatic models and lipopolysaccharide (LPS) -treated RAW264.7 cell with a comprehensive series of evaluations, including HE, PAS and Masson staining of lung histopathology, immunohistochemical staining, immunofluorescence technology, qRT-PCR, Western Blot, and ELISA inflammatory factor analysis. The results revealed M1 macrophage polarization in obesity-related asthmatic lung tissue alongside downregulation of AMPK expression. Under LPS stimulation, exogenous AMPK activation attenuated M1 macrophage polarization via the Janus kinase 2/ signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway. Additionally, in obesity-related asthmatic mice, AMPK activation was found to alleviate airway inflammation by regulating M1 macrophage polarization, the mechanism closely associated with the JAK2/STAT3 pathway. These findings not only advance our understanding of macrophage polarization in obesity-related asthma, but also provide new therapeutic targets for its treatment.

Anti-inflammatory activities of novel heat shock protein 90 isoform selective inhibitors in BV-2 microglial cells

Heat shock protein 90 (Hsp90) is a family of chaperone proteins that consists of four isoforms: Hsp90α, Hsp90β, glucose-regulated protein 94 (Grp94), and tumor necrosis factor type 1 receptor-associated protein (TRAP1). They are involved in modulating the folding, maturation, and activation of their client proteins to regulate numerous intracellular signaling pathways. Previous studies demonstrated that pan-Hsp90 inhibitors reduce inflammatory signaling pathways resulting in a reduction of inflammation and pain but show toxicities in cancer-related clinical trials. Further, the role of Hsp90 isoforms in inflammation remains poorly understood. This study aimed to determine anti-inflammatory activities of Hsp90 isoforms selective inhibitors on the lipopolysaccharide (LPS)-induced inflammation in BV-2 cells, a murine microglial cell line. The production of inflammatory mediators such as nitric oxide (NO), interleukin 1 beta (IL-1β), and tumor necrosis factor-alpha (TNF-α) was measured. We also investigated the impact of Hsp90 isoform inhibitors on the activation of nuclear factor kappa B (NF-κB), nuclear factor erythroid 2-related factor 2 (Nrf2), and mitogen-activated protein kinases (MAPKs). We found that selective inhibitors of Hsp90β reduced the LPS-induced production of NO, IL-1β, and TNF-α via diminishing the activation of NF-κB and Extracellular signal-regulated kinases (ERK) MAPK. The Hsp90α, Grp94, TRAP1 inhibitors had limited effect on the production of inflammatory mediators. These findings suggest that Hsp90β is the key player in LPS-induced neuroinflammation. Thereby providing a more selective drug target for development of medications involved in pain management that can potentially contribute to the reduction of adverse side effects associated with Hsp90 pan inhibitors.

An Engineered Bionic Nanoparticle Sponge as a Cytokine Trap and Reactive Oxygen Species Scavenger to Relieve Disc Degeneration and Discogenic Pain

The progressive worsening of disc degeneration and related nonspecific back pain are prominent clinical issues that cause a tremendous economic burden. Activation of reactive oxygen species (ROS) related inflammation is a primary pathophysiologic change in degenerative disc lesions. This pathological state is associated with M1 macrophages, apoptosis of nucleus pulposus cells (NPC), and the ingrowth of pain-related sensory nerves. To address the pathological issues of disc degeneration and discogenic pain, we developed MnO2@TMNP, a nanomaterial that encapsulated MnO2 nanoparticles with a TrkA-overexpressed macrophage cell membrane (TMNP). Consequently, this engineered nanomaterial showed high efficiency in binding various inflammatory factors and nerve growth factors, which inhibited inflammation-induced NPC apoptosis, matrix degradation, and nerve ingrowth. Furthermore, the macrophage cell membrane provided specific targeting to macrophages for the delivery of MnO2 nanoparticles. MnO2 nanoparticles in macrophages effectively scavenged intracellular ROS and prevented M1 polarization. Supportively, we found that MnO2@TMNP prevented disc inflammation and promoted matrix regeneration, leading to downregulated disc degenerative grades in the rat injured disc model. Both mechanical and thermal hyperalgesia were alleviated by MnO2@TMNP, which was attributed to the reduced calcitonin gene-related peptide (CGRP) and substance P expression in the dorsal root ganglion and the downregulated Glial Fibrillary Acidic Protein (GFAP) and Fos Proto-Oncogene (c-FOS) signaling in the spinal cord. We confirmed that the MnO2@TMNP nanomaterial alleviated the inflammatory immune microenvironment of intervertebral discs and the progression of disc degeneration, resulting in relieved discogenic pain.

Bardoxolone methyl breaks the vicious cycle between M1 macrophages and senescent nucleus pulposus cells through the Nrf2/STING/NF-κB pathway

Intervertebral disc (IVD) degeneration (IDD), an age-related degenerative disease, is accompanied by the accumulation of senescent nucleus pulposus (NP) cells and extracellular matrix (ECM) degradation. The current study aims to clarify the role of M1 macrophages in the senescence of NP cells, and further explores whether bardoxolone methyl (CDDO-Me) can alleviate the pathological changes induced by M1 macrophages and relieve IDD. On the one hand, conditioned medium (CM) of M1 macrophages (M1CM) triggered senescence of NP cells and ECM degradation in a time-dependent manner. On the other hand, CM of senescent NP cells (S-NPCM) was collected to treat macrophages and we found that S-NPCM promoted the migration and M1-polarization of macrophages. However, both of the above effects can be partially blocked by CDDO-Me. We further explored the mechanism and found that M1CM promoted the expression level of STING and nuclear translocation of P65 in NP cells, while being restrained by CDDO-Me and STING inhibitor H151. In addition, the employment of Nrf2 inhibitor ML385 facilitated the expression level of STING and nuclear translocation of P65, thereby blocking the effects of CDDO-Me on suppressing senescence of NP cells and ECM degradation. In vivo, the injection of CDDO-Me into the disc decreased the infiltration of M1 macrophages and ameliorated degenerative manifestations in the puncture-induced rat IDD model. In conclusion, CDDO-Me was proved to break the vicious cycle between M1 macrophages and senescent NP cells through the Nrf2/STING/NF-κB pathway, thereby attenuating the progression of IDD.

HSP90, a Common Therapeutic Target for Suppressing Skin Injury Caused by Exposure to Chemically Diverse Classes of Blistering Agents

Vesicants such as arsenicals and mustards produce highly painful cutaneous inflammatory and blistering responses, hence developed as chemical weapons during World War I/II. Here, using lewisite and sulfur mustard surrogates, namely phenylarsine oxide (PAO) and 2-chloroethyl ethyl sulfide (CEES), respectively, we defined a common underlying mechanism of toxic action by these two distinct classes of vesicants. Murine skin exposure to these chemicals causes tissue destruction characterized by increase in skin bifold thickness, Draize score, infiltration of inflammatory cells, and apoptosis of epidermal and dermal cells. RNA sequencing analysis identified ∼346 inflammatory genes that were commonly altered by both PAO and CEES, along with the identification of cytokine signaling activation as the top canonical pathway. Activation of several proinflammatory genes and pathways is associated with phosphorylation-dependent activation of heat shock protein 90α (p-HSP90α). Topical treatment with known HSP90 inhibitors SNX-5422 and IPI-504 post PAO or CEES skin challenge significantly attenuated skin damage including reduction in overall skin injury and clinical scores. In addition, highly upregulated inflammatory genes Saa3, Cxcl1, Ccl7, IL-6, Nlrp3, Csf3, Chil3, etc. by both PAO and CEES were significantly diminished by treatment with HSP90 inhibitors. These drugs not only reduced PAO- or CEES-induced p-HSP90α expression but also its client proteins NLRP3 and pP38 and the expression of their target inflammatory genes. Our data confirm a critical role of HSP90 as a shared underlying molecular target of toxicity by these two distinct vesicants and provide an effective and novel medical countermeasure to suppress vesicant-induced skin injury. SIGNIFICANCE STATEMENT: Development of effective and novel mechanism-based antidotes that can simultaneously block cutaneous toxic manifestations of distinct vesicants is important and urgently needed. Due to difficulties in determining the exact nature of onsite chemical exposure, a potent drug that can suppress widespread cutaneous damage may find great utility. Thus, this study identified HSP90 as a common molecular regulator of cutaneous inflammation and injury by two distinct warfare vesicants, arsenicals and mustards, and HSP90 inhibitors afford significant protection against skin damage.

Identification of a novel, MSC-induced macrophage subtype via single-cell sequencing: implications for intervertebral disc degeneration therapy

Intervertebral disc (IVD) degeneration is a common pathological condition associated with low back pain. Recent evidence suggests that mesenchymal signaling cells (MSCs) promote IVD regeneration, but underlying mechanisms remain poorly defined. One postulated mechanism is via modulation of macrophage phenotypes. In this manuscript, we tested the hypothesis that MSCs produce trophic factors that alter macrophage subsets. To this end, we collected conditioned medium from human, bone marrow-derived STRO3+ MSCs. We then cultured human bone marrow-derived macrophages in MSC conditioned medium (CM) and performed single cell RNA-sequencing. Comparative analyses between macrophages cultured in hypoxic and normoxic MSC CM showed large overlap between macrophage subsets; however, we identified a unique hypoxic MSC CM-induced macrophage cluster. To determine if factors from MSC CM simulated effects of the anti-inflammatory cytokine IL-4, we integrated the data from macrophages cultured in hypoxic MSC CM with and without IL-4 addition. Integration of these data sets showed considerable overlap, demonstrating that hypoxic MSC CM simulates the effects of IL-4. Interestingly, macrophages cultured in normoxic MSC CM in the absence of IL-4 did not significantly contribute to the unique cluster within our comparison analyses and showed differential TGF-β signaling; thus, normoxic conditions did not approximate IL-4. In addition, TGF-β neutralization partially limited the effects of MSC CM. In conclusion, our study identified a unique macrophage subset induced by MSCs within hypoxic conditions and supports that MSCs alter macrophage phenotypes through TGF-β-dependent mechanisms.

Analysis of global research hotspots and trends in immune cells in intervertebral disc degeneration: A bibliometric study

Intervertebral disc degeneration is an important pathological basis for spinal degenerative diseases. The imbalance of the immune microenvironment and the involvement of immune cells has been shown to lead to nucleus pulposus cells death. This article presents a bibliometric analysis of studies on immune cells in IDD in order to clarify the current status and hotspots. We searched the WOSCC, Scopus and PubMed databases from 01/01/2001 to 08/03/2023. We analyzed and visualized the content using software such as Citespace, Vosviewer and the bibliometrix. This study found that the number of annual publications is increasing year on year. The journal study found that Spine had the highest number of articles and citations. The country/regions analysis showed that China had the highest number of publications, the USA had the highest number of citations and total link strength. The institutional analysis found that Shanghai Jiao Tong University and Huazhong University of Science Technology had the highest number of publications, Tokai University had the highest citations, and the University of Bern had the highest total link strength. Sakai D and Risbud MV had the highest number of publications. Sakai D had the highest total link strength, and Risbud MV had the highest number of citations. The results of the keyword analysis suggested that the current research hotspots and future directions continue to be the study of the mechanisms of immune cells in IDD, the therapeutic role of immune cells in IDD and the role of immune cells in tissue engineering for IDD.

Degenerated nucleus pulposus cells derived exosome carrying miR-27a-3p aggravates intervertebral disc degeneration by inducing M1 polarization of macrophages

BACKGROUND

Intervertebral disc degeneration (IVDD) is a major contributor to spinal disorders. Previous studies have indicated that the infiltration of immunocytes, specifically macrophages, plays a crucial role in the advancement of IVDD. Exosomes (exo) are believed to play a significant role in intercellular communication. This study aims to investigate the role of exosomes derived from degenerated nucleus pulposus (dNPc) in the process of macrophages M1 polarization.

METHODS

Nucleus pulposus (NP) tissue and nucleus pulposus cells (NPc) were collected from patients with intervertebral disc degeneration (IVDD) and idiopathic scoliosis. Immunohistochemistry analysis was performed to determine the number of M1 macrophages in NP tissue. Subsequently, exosomes derived from degenerated NP cells (dNPc-exo) and non-degenerated NP cells (nNPc-exo) were collected and co-cultured with M0 macrophages, which were induced from THP-1 cells. The M1 phenotype was assessed using western blot, flow cytometry, immunofluorescence staining, and qRT-PCR. RNA-sequencing analysis was conducted to examine the expression levels of microRNAs in the dNPc-exo and nNPc-exo groups, and qRT-PCR was performed to investigate the effect pf different microRNA to induce macrophage polarization. Furthermore, western blot and qRT-PCR were employed to demonstrate the regulatory effect of microRNAs carried by dNPc-exo on downstream target signaling pathways in macrophages. Finally, an animal model of IVDD was utilized to investigate the impact of dNPc-exo on inducing M1 polarization of macrophages and its role in the IVDD process.

RESULTS

In this study, we observed an increase in the number of M1 macrophages as the intervertebral disc (IVD) degraded. Additionally, we discovered that dNPc releases exosomes (dNPc-exo) could promote the polarization of macrophages towards the M1 phenotype. Notably, through RNA-sequencing analysis of dNPc-exo and nNPc-exo groups, we identified miR-27a-3p as a highly expressed miRNA in the dNPc-exo group, which significantly influences the induction of M1 polarization of macrophages. And then, we discovered that dNPc-exo has the ability to transport miR-27a-3p and target the PPARγ/NFκB/PI3K/AKT signaling pathway, thereby influencing the M1 polarization of macrophages. We conducted experiments using rat model of IVDD and observed that the exosomes carrying miR-27a-3p actually induced the M1 polarization of macrophages and exacerbated the degradation of IVD.

CONCLUSION

In conclusion, our findings highlight the significant role of dNPc-exo in IVDD process and provide a basis for further investigation into the mechanism of IVDD and the potential of exosome-based therapy.

CX3CL1/CX3CR1 axis alleviates inflammation and apoptosis in human nucleus pulpous cells via M2 macrophage polarization

CX3C chemokine ligand 1 (CX3CL1) belongs to the CX3C chemokine family and is involved in various disease processes. However, its role in intervertebral disc degeneration (IDD) remains to be elucidated. In the present study, western blotting, reverse transcription-quantitative PCR and ELISA assays were used to assess target gene expression. In addition, immunofluorescence and TUNEL staining were used to assess macrophage infiltration, monocyte migration and apoptosis. The present study aimed to reveal if and how CX3CL1 regulates IDD progression by exploring its effect on macrophage polarization and apoptosis of human nucleus pulposus cells (HNPCs). The data showed that CX3CL1 bound to CX3C motif chemokine receptor 1 (CX3CR1) promoted the M2 phenotype polarization via JAK2/STAT3 signaling, followed by increasing the secretion of anti-inflammatory cytokines from HNPCs. In addition, HNPC-derived CX3CL1 promoted M2 macrophage-derived C-C motif chemokine ligand 17 release thereby reducing the apoptosis of HNPCs. In clinic, the reduction of mRNA and protein levels CX3CL1 in degenerative nucleus pulposus tissues (NPs) was measured. Increased M1 macrophages and pro-inflammatory cytokines were found in NPs of IDD patients with low CX3CL1 expression. Collectively, these findings suggested that the CX3CL1/CX3CR1 axis alleviates IDD by reducing inflammation and apoptosis of HNPCs via macrophages. Therefore, targeting CX3CL1/CX3CR1 axis is expected to produce a new therapeutic approach for IDD.

Comprehensive pan-cancer analysis of STAT3 as a prognostic and immunological biomarker

Numerous studies have indicated that STAT3 plays a key role in promoting oncogenesis and it is considered a potential therapeutic target for cancer treatment; however, there are no reports on STAT3 using pan-cancer analysis. Therefore, it is important to investigate the role of STAT3 in different types of tumors using pan-cancer analysis. In the present study, we used multiple databases to comprehensively analyze the relationship between STAT3 expression and prognosis, different stages of patients with cancer, investigate the clinical value of STAT3 in predicting prognosis, and the relationship between STAT3 genetic alteration and prognosis, drug sensitivity, and STAT3 expression, to determine whether STAT3 participates in tumor immunity, to provide a rationale for STAT3 as a treatment target for a broad-spectrum malignancies. Our results indicate that STAT3 can serve as a prognostic, sensitivity prediction biomarker and a target for immunotherapy, which has been of great value for pan-cancer treatment. Overall, we found that STAT3 significantly predicted cancer prognosis, drug resistance, and immunotherapy, providing a rationale for further experimental studies.

HSP90β promotes osteoclastogenesis by dual-activation of cholesterol synthesis and NF-κB signaling

Heat shock protein 90β (Hsp90β, encoded by Hsp90ab1 gene) is the most abundant proteins in the cells and contributes to variety of biological processes including metabolism, cell growth and neural functions. However, genetic evidences showing Hsp90β in vivo functions using tissue specific knockout mice are still lacking. Here, we showed that Hsp90β exerted paralogue-specific role in osteoclastogenesis. Using myeloid-specific Hsp90ab1 knockout mice, we provided the first genetic evidence showing the in vivo function of Hsp90β. Hsp90β binds to Ikkβ and reduces its ubiquitylation and proteasomal degradation, thus leading to activated NF-κB signaling. Meanwhile, Hsp90β increases cholesterol biosynthesis by activating Srebp2. Both pathways promote osteoclastogenic genes expression. Genetic deletion of Hsp90ab1 in osteoclast or pharmacological inhibition of Hsp90β alleviates bone loss in ovariectomy-induced mice. Therefore, Hsp90β is a promising druggable target for the treatment of osteoporosis.

Macrophages and Intervertebral Disc Degeneration

The intervertebral disc (IVD) aids in motion and acts to absorb energy transmitted to the spine. With little inherent regenerative capacity, degeneration of the intervertebral disc results in intervertebral disc disease, which contributes to low back pain and significant disability in many individuals. Increasing evidence suggests that IVD degeneration is a disease of the whole joint that is associated with significant inflammation. Moreover, studies show elevated macrophage accumulation within the IVD with increasing levels of disease severity; however, we still need to understand the roles, be they causative or consequential, of macrophages during the degenerative process. In this narrative review, we discuss hallmarks of IVD degeneration, showcase evidence of macrophage involvement during disc degeneration, and explore burgeoning research aimed at understanding the molecular pathways regulating macrophage functions during intervertebral disc degeneration.

Immune exposure: how macrophages interact with the nucleus pulposus

Intervertebral disc degeneration (IDD) is a primary contributor to low back pain. Immune cells play an extremely important role in modulating the progression of IDD by interacting with disc nucleus pulposus (NP) cells and extracellular matrix (ECM). Encased within the annulus fibrosus, healthy NP is an avascular and immune-privileged tissue that does not normally interact with macrophages. However, under pathological conditions in which neovascularization is established in the damaged disc, NP establishes extensive crosstalk with macrophages, leading to different outcomes depending on the different microenvironmental stimuli. M1 macrophages are a class of immune cells that are predominantly pro-inflammatory and promote inflammation and ECM degradation in the NP, creating a vicious cycle of matrix catabolism that drives IDD. In contrast, NP cells interacting with M2 macrophages promote disc tissue ECM remodeling and repair as M2 macrophages are primarily involved in anti-inflammatory cellular responses. Hence, depending on the crosstalk between NP and the type of immune cells (M1 vs. M2), the overall effects on IDD could be detrimental or regenerative. Drug or surgical treatment of IDD can modulate this crosstalk and hence the different treatment outcomes. This review comprehensively summarizes the interaction between macrophages and NP, aiming to highlight the important role of immunology in disc degeneration.

Update on the roles of macrophages in the degeneration and repair process of intervertebral discs

Intervertebral disc (IVD) degeneration is the common cause of lumbar degenerative diseases, causing severe social and economic burden. The process of IVD degeneration involves a complex of pathologic changes on both extracellular matrix degradation and resident cell apoptosis. In recent years, there is increasing evidence that macrophages play vital roles during the damage and repair process of IVD degeneration. Nevertheless, the interactions between macrophages and IVD are not well understood, even if the IVD has long been regarded as the immune privileged site. Therefore, this review mainly focuses on the progress and obstacles of studies investigating the blood supply, immune response and especially macrophages during the IVD degeneration process.

New Progress in Basic Research of Macrophages in the Pathogenesis and Treatment of Low Back Pain

Low back pain (LBP) is quite common in clinical practice, which can lead to long-term bed rest or even disability. It is a worldwide health problem remains to be solved. LBP can be induced or exacerbated by abnormal structure and function of spinal tissue such as intervertebral disc (IVD), dorsal root ganglion (DRG) and muscle; IVD degeneration (IVDD) is considered as the most important among all the pathogenic factors. Inflammation, immune response, mechanical load, and hypoxia etc., can induce LBP by affecting the spinal tissue, among which inflammation and immune response are the key link. Inflammation and immune response play a double-edged sword role in LBP. As the main phagocytic cells in the body, macrophages are closely related to body homeostasis and various diseases. Recent studies have shown that macrophages are the only inflammatory cells that can penetrate the closed nucleus pulposus, expressed in various structures of the IVD, and the number is positively correlated with the degree of IVDD. Moreover, macrophages play a phagocytosis role or regulate the metabolism of DRG and muscle tissues through neuro-immune mechanism, while the imbalance of macrophages polarization will lead to more inflammatory factors to chemotaxis and aggregation, forming an "inflammatory waterfall" effect similar to "positive feedback," which greatly aggravates LBP. Regulation of macrophages migration and polarization, inhibition of inflammation and continuous activation of immune response by molecular biological technology can markedly improve the inflammatory microenvironment, and thus effectively prevent and treat LBP. Studies on macrophages and LBP were mainly focused in the last 3-5 years, attracting more and more scholars' attention. This paper summarizes the new research progress of macrophages in the pathogenesis and treatment of LBP, aiming to provide an important clinical prevention and treatment strategy for LBP.